Objective: The purpose of this study was to determine the instructional characteristics of online continuing dental education courses on the World Wide Web. Method and materials: One hundred fifty-seven online courses offered by 32 providers were reviewed for 34 criteria. Results: Courses of various types spanned a variety of topics. Approximately half of all courses offered continuing dental education credit. The relationship between credit hours and course length was quite variable. Most courses consisted of text and images. Very few courses used advanced media such as video clips. Measured against an index of instructional quality developed for this study, the instructional quality of the courses, in general, was poor. Most for-credit courses contained self-assessment questions, but only 28% of courses scored the questions online. Basic information that was missing on many courses included the authors' names (29%); the intended audience (81%); goals and objectives (77%); and references (85%). In 47% of the courses, there was no opportunity to provide feedback to either the author or the provider. Conclusion: The theoretical advantages of Web-based continuing dental education are numerous, but the currently available online resources are mostly of unacceptable quality.