Background: Clinical supervisors have several different responsibilities. Although their responsibilities as an assessor are important, little is known about what skill set should be acquired for this role and how to foster their development. Documenting assessor skills to study their acquisition and development is critical. Methods: A web survey based on the principles of Appreciative Inquiry was distributed to faculty members and residents from a Department of Medicine at a Canadian University. Participants were asked to list five and then to identify five (from a list of 10) characteristics or skills demonstrated by clinical supervisors recognised for their excellent assessment skills. Results: Seventeen per cent of faculty members and 23 per cent of residents completed the survey. Fairness is perceived as a key characteristic of an excellent assessor. Faculty members consider that appropriate medical knowledge and skills are important. Residents expressed the importance of appropriate feedback. Both groups indicated the importance of direct observation as a basis for assessment. Discussion: This study offers preliminary insights into the characteristics of excellent assessors. Given the importance of assessment in the daily activities of clinical supervisors, research efforts should strive to better characterise this role in the hopes of increasing the quality and accuracy of assessment.