Background: Medical students increasingly participate in rotations in primary care settings, such as general practices. Although general practices can differ markedly from hospital settings, research on the instructional quality of general practice rotations is relatively scarce. Aim: We conducted a study to identify which aspects make a significant contribution to the instructional quality of general practice clerkships, as perceived by students. Method: After completing their general practice attachment, 155 fifth-year medical students filled out an evaluation questionnaire. Exploratory factor analysis and reliability analysis identified clusters of correlated independent variables. Subsequent regression analysis revealed the relations between the reduced set of independent variables and the dependent variable 'Instructional quality'. Results: Both the quality of supervision and the size and diversity of the patient mix substantially affected students' experienced instructional quality. Opportunities and facilities to perform independently were correlated with instructional quality, but did not affect the instructiveness directly. Conclusions: Supervision, patient mix and independence are crucial factors for learning in general practice. This is consistent with findings in hospital settings. The perceived quality of instruction hinges on supervision, which is not only the variable most strongly related to instructional quality, but which also affects both the patient mix and students' independence.