We prospectively studied the relationship between interdisciplinary collaboration and patient outcomes in the medical intensive care unit (MICU) using nurses' and residents' reports of amount of collaboration involved in making decisions about transferring patients from the MICU to a unit with a less intense level of care. Either readmission to the MICU or death was considered a negative patient outcome. Nurses' reports of collaboration were significantly (p = 0.02) and positively associated with patient outcome, controlling for severity of illness. Patient predicted risk of negative outcome decreased from 16%, when the nurse reported no collaboration in decision making, to 5% when the process was fully collaborative. There was an interaction of collaboration with availability of alternative choices in the transfer decision-making situation. When alternatives were available, collaboration was more strongly associated with patient outcome. There was no significant relationship between residents' reports of collaboration and patient outcomes. The correlation between amount of collaboration reported by nurses and residents about the same decisions was quite low (r = 0.10).