OBJECTIVE: The objective of this study was to determine the number and topical range of available online medical books and to assess how health sciences libraries were providing access to these resources on their public Websites. METHOD: The collection-based evaluative technique of list checking was used to assess the number and topical range of online medical books of the six largest publishers. Publisher inventory lists were downloaded over a two-day period (May 16-17, 2004). Titles were counted and compared with the 2003 Brandon/Hill list. A sample of health sciences libraries was subsequently derived by consulting the 2004 "Top Medical Schools-Research" in U.S. News & World Report. Bibliographic and bibliothecal access methods were evaluated based on an inspection of the publicly available Websites of the sample libraries. RESULTS: Of 318 currently published online medical books, 151 (47%) were Brandon/Hill titles covering 42 of 59 Brandon/Hill topics (71%). These 151 titles represented 22% (N = 672) of the Brandon/Hill list, which further broke down as 52 minimal core, 41 initial purchase, and 58 other recommended Brandon/Hill titles. These numbers represented 50%, 28%, and 12%, respectively, of all Brandon/Hill titles corresponding to those categories. In terms of bibliographic access, 20 of 21 of sampled libraries created catalog records for their online medical books, 1 of which also provided analytical access at the chapter level, and none provided access at the chapter section level. Of the 21 libraries, 19 had library Website search engines that provided title-level access and 4 provided access at the chapter level and none that at the chapter section level. For bibliothecal access, 19 of 21 libraries provided title-level access to medical books, 8 of which provided classified and alphabetic arrangements, 1 provided a classified arrangement only, and 10 provided an alphabetic arrangement only. No library provided a bibliothecal arrangement for medical book chapters or chapter sections. CONCLUSIONS: This study shows that the number and topical range of online medical books is reaching a point where collection-level consideration is warranted to facilitate efficient use and to prevent the problem of split files. However, the results also show that few efforts are underway on the publicly available Websites of the surveyed health sciences libraries to provide the analytical access necessary to meet the structural needs of clinical information seekers.