PURPOSE: Few studies have compared the instructiveness of real patient contacts with simulated patient (SP) contacts. Although most of these studies found no difference, students often comment that the instructiveness of both encounters is dissimilar. The aims of this study were to evaluate which contact (real patient or SP) is perceived as most instructive by students and which variables contribute to this. METHOD: The authors performed an experiment involving 163 first-year medical students, randomized to having a real patient contact (n = 61) or SP contact (n = 102). Quantitative (questionnaires) and qualitative (focus groups) methods were used to evaluate the perceived instructiveness of the contact. RESULTS: The general instructiveness of both real patient contacts and SP contacts was marked high. Several differences between the evaluations of real patient contacts and SP contacts were found. For example, students considered real patient contacts less helpful in practicing communication skills and considered the real patients' feedback less relevant. The focus group interviews yielded explanations for many of the differences found. Students regarded real patients as more authentic. However, SPs were better informed about the purpose of the consultation and provided the student with more specific feedback. CONCLUSIONS: Students consider authenticity an important advantage of real patients. Their difficult recruitment is an important disadvantage, however, SPs have important advantages compared with real patients--for example, their feedback. The choice of real patient contacts or SP contacts for medical education depends on factors like the phase of the curriculum and the aim of the encounter.