Objective: To examine the process and information used by medical directors (MDs) of private health plans to make medical coverage determinations for new medical technologies, and to assess the influence of plan characteristics on the process., Design: Cross-sectional national survey., Participants: Two hundred thirty-one MDs at private health plans representing 66% and 72% of the US population covered by HMOs and indemnity plans, respectively., Measurements: Actual and optimal review process, final decision authority, sources, and evidence used for technology coverage decisions., Results: In 96% of plans, MDs take part in the medical policy review process for new technology. However, MDs have final authority over coverage decisions in only 27% of plans. Indemnity plans are more likely to assert that MDs should be responsible for final decisions, odds ration (OR) = 3.3 (95% confidence interval [95% CI] 1.4, 10). Optimal sources of information of new technology were journals, medical society statements or practice guidelines, and opinions of national experts. Actual sources of information used differed from optimal ones; local experts were used more often than is considered optimal (p < .001). For-profit plans were more likely than nonprofit plans to use national experts, OR 2.5 (95% CI 1.3, 5.0), and practice guidelines, OR 5.0 (95% CI 2.5, 10). Randomized trials (94% of MDs) meta-analyses (61%), and reviews (42%) were considered the best evidence for making coverage decisions. Barriers to making optimal decisions were lack of timely evidence on effectiveness and cost-effectiveness, not legal or regulatory issues; HMO, small, and nonprofit plans were two or three times more likely to list lack of cost-effectiveness data than their counterparts (p < .05)., Conclusions: Although MDs are nearly always involved in the technology evaluation process, a minority of MDs retain final authority over coverage decisions. Evidence from strong scientific research designs is the most frequently cited basis for decisions, but there is need for more timely, rigorous scientific evidence on medical interventions. How a health plan evaluates a new medical technology for coverage varies with identifiable plan characteristics.