The serratus anterior plane block (SAPB) is an ultrasound-guided compartment block; limited data suggest that it can decrease pain in patients with rib fractures or chest wall pain. We sought to determine the effect of SAPB on pain and incentive spirometry (IS) maximal vital capacity in adult patients with rib fractures.We enrolled a prospective sample of adult patients with at least two unilateral rib fractures who were being admitted for pain control. SAPB was performed by trained emergency physicians. Patients reported pain on an 11-point Numeric Rating Scale at rest and during IS, before, 15, and 60 minutes after SAPB.Mean pain scores decreased by 1.8 (SD 2.17, 95% confidence interval [CI]: 0.79-2.81) at 15 minutes and 2.5 (SD 2.69, 95% CI: 1.24-3.76) at 60 minutes. Compared to pre-block pain scores during IS, mean pain scores decreased by 1.95 (SD 1.99, 95% CI: 1.02-2.88) at 15 minutes and 2.4 (SD 2.42, 95% CI: 1.27-3.53) at 60 minutes. Mean maximum vital capacity increased by 232 mL (SD 406, 95% CI: 36-427) at 60 minutes. Zero SAPB-attributable complications were identified in the 24 hours post-enrollment.In patients with multiple rib fractures, SAPB reduced pain scores at rest and during IS, and increased maximal vital capacity. The SABP may be a safe and effective modality for pain control in trauma patients with multiple rib fractures.