One year after implementation of a new schedule of summative assessment of professional attitude and conduct (AC) for medical undergraduates at the University of Wales College of Medicine (UWCM), we evaluated its effectiveness and obtained feedback of the perceptions of participating teachers and students. An anonymous questionnaire was administered to all 4th year students and their clinical teachers. Four out of 180 students actually failed to complete the 4th year as a result of unsatisfactory AC. Of these, three students were identified as having a problem which benefited from supportive remediation. One hundred and twenty out of 244 (49%) teachers and 166 out of 195 (85%) students completed the feedback questionnaires. The majority of students and teachers agreed that AC should be an integral part of their assessment. However, several problems were highlighted, in particular, students' perception that marks were sometimes based on assessment of knowledge rather than attitude and conduct and teachers' reluctance to identify unprofessional behaviour in students. The use of longitudinal assessment of professional AC was found to be effective at identifying students with persistent AC problems and also provided an opportunity for formative experience. The reluctance of teachers to identify negative behaviours, compared to deficiencies in skill and knowledge, is an important aspect of developing a reliable method of evaluating professional attitudes.