An interactive computer-assisted learning (CAL) module on glomerulonephritis, previously identified by fourth-year medical students as a difficult topic, was developed. The module comprised background material, case studies, graphics, animation, video and supporting quizzes with feedback. The impact of the module on student learning was evaluated by comparing the performance of two matched groups of students, only one of which accessed the CAL module, in an online assessment. The analysis examined the effect of having completed a clinical term in renal medicine. A significant improvement in the performance of those students who used the CAL module was demonstrated. Unexpectedly, completing a renal medicine term had no beneficial influence on students' performance. Students who used the CAL module perceived a significant decrease in the difficulty of the topic. It is concluded that the module is an effective learning tool, but important caveats are noted associated with using CAL modules in redesigned medical curricula.