Clear communication is considered the sine qua non of effective teamwork. Breakdowns in communication resulting from interprofessional conflict are believed to potentiate errors in the care of patients, although there is little supportive empirical evidence. In 1999, we surveyed a national, multi-specialty sample of 6,106 residents (64.2% response rate). Three questions inquired about "serious conflict" with another staff member. Residents were also asked whether they had made a "significant medical error" (SME) during their current year of training, and whether this resulted in an "adverse patient outcome" (APO). Just over 20% (n = 722) reported "serious conflict" with another staff member. Ten percent involved another resident, 8.3% supervisory faculty, and 8.9% nursing staff. Of the 2,813 residents reporting no conflict with other professional colleagues, 669, or 23.8%, recorded having made an SME, with 3.4% APOs. By contrast, the 523 residents who reported conflict with at least one other professional had 36.4% SMEs and 8.3% APOs. For the 187 reporting conflict with two or more other professionals, the SME rate was 51%, with 16% APOs. The empirical association between interprofessional conflict and medical errors is both alarming and intriguing, although the exact nature of this relationship cannot currently be determined from these data. Several theoretical constructs are advanced to assist our thinking about this complex issue.