Relatively little is known about the effectiveness of Web-based learning (WBL) in medical education and how it compares to conventional methods. This study examined the influence of an interactive, online curriculum in a third-year medical school family medicine clerkship on students' ability to create a management plan for a patient newly diagnosed with type 2 diabetes. We also evaluated how the online curriculum compared to a conventionally taught curriculum. The online course included three integrated activities: (1) self-study modules, (2) a patient case study, and (3) a moderated discussion board for posting and discussing patient care plans. The WBL curriculum was compared to small-group case-based sessions with a faculty facilitator. Students completed a test case before and after the clerkship. Among standard-of-care diabetic management interventions not ordered on the pretest, 38% were subsequently correctly ordered by WBL students on the posttest, versus 33% by students in the comparison group. For four out of five subgroups assessed on the case write-ups, the gain from before to after the clerkship favored the WBL group. Improvement among students learning online exceeded that of students learning face to face. This suggests superiority of the online method, a finding consistent with other recently published, well-controlled studies.