An instrument has been developed to assess tutor performance in problem-based tutorial groups. This tutor evaluation questionnaire consists of 13 statements reflecting the tutor's behaviour. The statements are based on a description of the tasks set for the tutor. This study reports results on the validity and reliability of the instrument. Confirmatory factor analysis showed that a three-factor model fitted the data reasonably well. The three factors are: (1) guiding students through the learning process, (2) content knowledge input, and (3) commitment to the group's learning. Generalizability studies indicated that the rating scales provide reliable information with student responses of existing tutorial group sizes. It is concluded that the tutor evaluation questionnaire is a fairly valid and reliable instrument that can be used in staff development programmes.