Background. To improve student skills specific to the evaluation of radiology studies during a required clerkship in surgery for 4th-year medical students, we initiated a self-study CD-ROM educational module midway through 2000-2001. We hypothesized that student performance would improve after implementation of this module and identified factors that predicted student performance. Materials and methods. Students (n = 98) chose one of two hospital sites for a clerkship that focuses on the care of acutely ill surgical patients. A standardized clinical final evaluation (Objective Structured Clinical Evaluation) contained two components: radiology (R score) and ICU clinical "flow sheet" interpretation (C score). We evaluated the effect of the CD-ROM educational module and other factors on student exam performance using univariate and multivariate analysis. Results. The site of the clerkship and use of the CDROM educational module were significant factors affecting the C score identified by ANOVA, P < 0.05. With the R scores from both sites combined, performance improved by 22% from a mean of 29.2 +/- 1.1 to 35.7 +/- 1.1 with use of the module. A stepwise multiple regression analysis testing the effect of site, time of year, educational module, and a prior radiology clerkship on the R score identified that the site and CD-ROM educational module modeled performance; R-2 = 0.30, P < 0.01. The C score was affected by site (A: 72.5 +/- 1.6 vs B: 67.3 +/- 1.9, P < 0.05 by ANOVA). Regression analysis identified that time of year (later associated with increased score) and prior performance on the 3rd-year standardized exams (OSCE and NBME) modeled 4th-year C score; R-2 = 0.20, P < 0.01. Conclusions. In a clerkship that already emphasized faculty-facilitated case-based learning, including evaluation of radiological studies, the addition of a self-study CD-ROM radiology module significantly improved test score. This study supports the efficacy of directed self-study to improve student skills. (C) 2002 Elsevier Science (USA).