Problem-based learning (PBL) as a new instructional method is becoming increasingly popular. PBL is hypothesized to have a number of advantages for learning because it applies insights from cognitive learning theory and it fosters a lifelong learning strategy. As in all learning programs there are individual differences between students. This study investigates individual differences in students' PBL behavior and its effect on achievement using 164 health sciences students in the Netherlands. PBL learning was measured using 24 vignettes of situational descriptions of PBL behavior. The students' behavior during a tutorial group meeting and during individual study were considered as PBL behavior. Results indicate that achievement is significantly influenced by the activity of PBL behavior after correction for more general test preparation behaviors. The style of PBL behavior did not yield a significant contribution. Given the statistically significant relationship found with one of the PBL behavior dimensions (activity), it would be valuable to study the effects of the dimensions of PBL style and activity on achievement in isolation and in combination. (Contains 1 figure, 4 tables, and 22 references.) (Author/SLD)