Clinical data gathering is central to clinical competence. Although research has demonstrated the value to experienced clinicians of information obtained from the history, little is known of how medical students use this information. In the present study, two case simulations (in rheumatoid arthritis and systemic lupus erythematosis) were developed to assess medical student information gathering and utilization. The results indicate that most of the students were already considering the correct diagnosis as a possibility after the presenting complaint and patient description. However, the medical history exerted the strongest influence on transforming the correct diagnosis from just another diagnostic possibility into the favored diagnostic candidate. Students who failed to list the correct diagnosis in the differential diagnosis after obtaining the history were significantly less likely to reach the correct diagnosis at the end of the case. These results confirm the critical importance of the history in medical problem solving.