Introduction: Physician use of the Internet for practice improvement has increased dramatically over the last decade, but research shows that many physicians choose not to participate. The current study investigated the association of specific physician characteristics with enrollment rates and intensity of participation in a specific Internet-delivered educational intervention to improve care to post-myocardial infarction (MI) patients. Methods: Primary-care physicians were recruited for participation in a randomized controlled trial designed to compare effectiveness of an intervention Web site versus a control Web site in the management of adult chronic disease. Physicians were informed that the intervention focused on ambulatory post-myocardial infarction patients. Physician characteristics were obtained from a commercial vendor with data merged from the American Medical Association and Alabama State Licensing Board. Enrollment and Web use were tracked electronically. Results: Out of a sample of 1337 eligible physicians, 177 (13.2%) enrolled in the study. Enrollment was higher for physicians with more post-MI patients (≥20 vs < 20 patients, 15.3% vs 9.3%, P = .002) and for those practicing in rural compared to urban areas (16.3% vs 12.1%, P = .046). Intensity of use of the Internet courses after initial enrollment was not predicted by physician characteristics in the current sample. Discussion: Physicians with more post-MI patients and rural practice location were found to predict enrollment in an Internet-delivered continuing medical education (CME) intervention designed to improve care for post-MI patients. These factors predicted program interest but not program use. More research is needed to replicate these findings to investigate variables that determine physician engagement in Internet CME. © 2009 The Alliance for Continuing Medical Education, the Society for Academic Continuing Medical Education, and the Council on CME, Association for Hospital Medical Education.