Purpose The aim of this paper is to provide evidence for the validity and reliability of a questionnaire for assessing the implementation of problem-based learning (PBL). This questionnaire was developed to assess the quality of PBL implementation from the perspective of medical school graduates. Methods: A confirmatory factor analysis was conducted to assess the validity of the questionnaire. The analysis was based on a survey of 225 graduates of a problem-based medical school in Indonesia. Results: The results showed that the confirmatory factor analysis model had a good fit to the data. Further, the values of the standardized loading estimates, the squared inter-construct correlations, the average variances extracted, and the composite reliabilities all provided evidence of construct validity. Conclusion: The PBL implementation questionnaire was found to be valid and reliable, making it suitable for evaluation purposes.