Introduction: The Colleges of Physicians and Surgeons of Alberta and Nova Scotia (CPSNS) use a standardized multisource feedback program, the Physician Achievement Review (PAR/NSPAR), to provide physicians with performance assessment data via questionnaires from medical colleagues, coworkers, and patients on 5 practice domains: consultation communication, patient interaction, professional self-management, clinical competence, and psychosocial management of patients. Physicians receive a confidential report; the intent is practice improvement. However, research indicates that feedback from medical colleagues appears to be less understood than that from coworkers or patients, due to a lack of specificity and concerns regarding feedback credibility. The purpose of this study was to determine how physicians make decisions about performance ratings for family physician (FP) colleagues in the 5 practice domains. Methods: This was an exploratory qualitative study using focus groups--one with 11 family physicians and one with 12 specialists--who had served as NSPAR "medical colleague" reviewers. We analyzed focus group transcripts using content analysis. Results: Family and specialist physicians provided examples of behaviors indicative of both high- and low-scoring performance for items within the 5 practice domains. From these, an assessment rubric was created to inform both external reviewers and the physicians being reviewed of performance expectations. Reviewers reported using varied sources of information to make assessments, including shared patients, medical records, referral letters, feedback from others, and self-reference. Discussion: The CPSNS has used the assessment rubric to create an online resource to inform medical colleague assessment and enhance the usefulness of their NSPAR scores. Further research will be required to determine its impact. (Contains 7 tables.)