Although nearly 18 million adults have been diagnosed as having a current alcohol abuse or dependence disorder, only 1 in 7 reports ever having received any kind of alcohol treatment (Grant et al., 2004; Cohen et al., 2007). At the same time, people with alcohol use problems are likely to be treated in trauma care centers and emergency departments (EDs) (Cohen et al., 2007) for problems related or unrelated to their alcohol use. People with alcohol-related problems are overrepresented in ED and primary care settings compared with those in the general population (Cherpitel, 1994). Furthermore, alcohol-related ED visits have increased significantly over the past 15 years (Cherpitel & Ye, 2012). Therefore, EDs provide an opportunity for screening and brief intervention for problematic alcohol use. Although it has been over three decades since a WHO Expert Committee first called for the development of methods that could be efficiently applied in primary care settings (World Health Organization, 1980), national goals for a reduction in substance-related ED visits (Healthy People 2010, U.S. Department of Health and Human Services, 2005) have not been realized (Cherpitel & Ye, 2012). A recent review (Nilsen et al., 2008) of 14 studies of brief motivational intervention (BMI) in EDs for alcohol indicates that although some studies have found that BMI reduced alcohol consumption, hazardous use of alcohol, and alcohol-related injuries (compared to usual ED care), approximately 35% of the reviewed studies found no effect (e.g. Daeppen, et al., 2007; D’Onofrio, et al., 2008). Also somewhat mixed are the results of a recent meta-analysis (Kaner et al., 2009) of 22 randomized controlled trials in primary care settings that confirmed the benefit of BMI for men but not women. Furthermore, even when positive treatment effects are reported, not all outcome measures are impacted similarly (e.g., Field et al., 2009; Monti et al., 1999). For example, past studies have identified BMI effects (i.e., group differences) in alcohol use but not in alcohol-related problems (Monti et al., 2007); others have found intervention group differences in alcohol-related problems, but not in drinking behaviors (Longabaugh et al., 2001; Monti et al., 1999). These discrepancies in results suggest the need for a more impactful approach. One possible avenue for enhancing the effects of BMI in emergency care might be to incorporate significant others (SO) into the treatment. Concerned SOs tend to be present soon after hospital admissions, and may be open to supporting their family member/friend’s behavior change. SOs can provide positive and/or negative influences on alcohol treatment process and outcome in various ways (Magill et al., 2010). For example, Havassy et al. (1991) found the social network can inhibit drinking; friends or family members can (a) provide feedback that might help motivate the problem drinker to change the drinking behavior; (b) affirm skills of the problem drinker that enhance the probability of successful change; (c) help set treatment goals; and (d) provide support for changes in drinking behavior (Miller et al., 1995a). On the negative side, an alcohol abuser’s social network is likely to include other heavy drinkers, and many will drink with their partners (e.g., Fernandez-Pol et al., 1986), which can make reducing alcohol intake or abstinence especially difficult (e.g., Havassy et al., 1991; Hunter-Reel et al., 2010), and can make it challenging to select an appropriate SO for intervention. Nevertheless, there is a basis for including SOs in brief alcohol treatment. There is a substantial literature establishing the efficacy of SO-enhanced interventions for alcohol problems (e.g., Epstein & McCrady, 1998; McCrady et al., 2009) although including SO’s in treatment does not always increase benefits (Monti, et al., 1990). Having family and friend networks that are supportive of alcohol use reduction is predictive of successful change (Longabaugh et al., 1995; Stout et al., 2012), with SO-involved alcohol interventions reliably increasing the likelihood that an at-risk drinker will initiate positive changes (O’Farrell, 1993). In a recent meta-analysis, a clear advantage was found for Behavioral Couples Treatment (BCT) over individual-based treatments for frequency and consequences of alcohol use as well as relationship satisfaction (Powers et al., 2008). Although the benefit of BCT with low severity problem drinkers has been studied less, there is some evidence for lower efficacy with these individuals (Powers et al., 2008). Miller and Rollnick (2002) support the notion that SOs are a natural support that can reinforce the identified patient’s change process. The Motivational Enhancement Therapy Manual created for Project MATCH (MET: Miller et al., 1992) suggests the inclusion of a SO in early treatment sessions to help patients resolve ambivalence regarding change. The premise was that SOs could describe alcohol-related consequences, offer support, comment on the feedback provided by the therapist, and generally contribute opinions that may be more positively received by the patient than if delivered by the therapist. Unfortunately, in Project MATCH only 17% of outpatient and 13% of aftercare MET patients elected to include SOs (Carroll et al., 1998), and only 2% did so in a subsequent study of MET (Miller et al., 2003a). Despite the number of studies examining and supporting BCT and couples treatment for alcohol use disorders, few studies incorporating SOs into motivational interviewing (MI) sessions have been conducted, and to date, such interventions have been delivered almost exclusively in individual format (cf. Cordova, et al., 2001). The efficacy of an enhanced MI that includes both the patient and a SO as a design element is unknown. Given the low rates of optional SO participation in prior research, any study designed to test the addition of SOs to MI sessions would necessarily have to require that both the patient and SO participate. It is likely that this requirement has been a deterrent to conducting this type of treatment study. Inherent difficulties and the additional work involved in recruiting appropriate SOs who are motivated to participate are indeed challenges. Nevertheless, given that SOs are often present and concerned about the patient in the hospital, recruitment and inclusion of SOs in such a study might be more successful in this “opportunistic setting.” Another variable that may influence outcomes is recruitment site. The efficacy of BMI has been studied most often in the ED, less often in the trauma unit, and very few studies have recruited patients from both sites. These treatment sites are distinct; trauma units treat more severely injured patients and over longer periods of time. Most trauma patients are hospitalized following acute treatment for the trauma; ED patients are not typically admitted to a trauma service. Both settings are appropriate for an opportunistic BMI as both provide a window of opportunity occasioned by a medical event (Field et al., 2010). Since the optimal application and practice of BIs in medical settings has been questioned (Field et al., 2010; Nilsen et al., 2009) this study enrolled patients from both sites. The objective of this study was to investigate the relative efficacy of a SO-enhanced Motivational Intervention (SOMI) compared to an Individual Motivational Intervention (IMI). Our primary aim was to test the hypothesis that patients who received SOMI would drink less alcohol and suffer fewer alcohol-related consequences in the year following their hospital visit as compared to patients assigned to IMI. Our secondary aim was to test the extent to which SOMI (compared to IMI) led to significant changes in SO behaviors related to patient drinking. Both sets of aims (primary and secondary) incorporated an exploration of the effects of intervention setting (trauma unit vs. ED) without a theoretical basis for hypothesizing any interaction.