Abstract Purpose To assess inter-rater agreement in perceptions of cases presented during Morbidity & Mortality conference (M&M) and changes associated with initiation of a modified M&M. Methods Faculty, residents, fellows, and students at weekly M&M between June 2001 and March 2002 voluntarily completed an anonymous questionnaire after each M&M case presentation, which asked: if the complication was avoidable (yes/no/not sure), if consensus was reached among participants (yes/no/not sure), the primary cause of the complication (diagnostic error, technical error, judgment error, nature of disease, other), when the primary cause occurred (preoperatively, intraoperatively, postoperatively), and which, if any, of 16 listed actions could prevent similar future problems. On September 24, 2001, the conference was lengthened and modified. Data collected before (n = 30 cases) and after M&M modification (n = 46 cases) were compared. Results A total of 76 cases were evaluated for a total of 860 completed forms. In 57 cases (75%), majority opinion (ie, ≥50% of participants) indicated that the complication resulted from either nature of disease (n = 32, 41%), or error in diagnosis (n = 5, 7%), technique (n = 8, 11%) or judgment (n = 12, 17%). There was no clear majority for the remainder of the cases. Relative to cases presented prior to M&M modification, for those presented post-modification, the majority perceived that consensus was reached more often (96% of cases vs. 70% of cases, p<.01), and that complications were more often avoidable (54% of cases vs. 23% of cases, p < .05), more likely caused during the preoperative period (26% of cases vs. 7% of cases, p < .01) and less likely caused during the postoperative period (28% of cases vs. 67% of cases, p < .01). Conclusions The variability in questionnaire responses suggests that an evaluation instrument such as that reported here can be useful in assessing educational needs, quantifying the efficacy of case presentations, and assessing the effects of modifications to conference content and structure. Modifying M&M in accordance with published recommendations appears to improve case analysis and consensus among participants.