To evaluate the rate of diagnostic errors leading to preventable deaths among patients admitted to our intensive care unit (ICU), we retrospectively reviewed the medical and autopsy records of all patients who died in the ICU between 1 January 1991 and 31 December 1993. Excluded were patients with traumatic injuries, cerebrovascular accidents and primary cardiac arrest. According to their length of stay (LOS) in the ICU, patients were subdivided into Group A (LOS 0-24 hours), Group B (LOS > 24 hours-14 days), and Group C (LOS > 14 days). Errors were divided into Type 1 (failure to recognize a treatable life-threatening condition); Type 2 (failure to recognize a life-threatening condition, which treated, however, would unlikely alter the outcome), and Type 3 (failure to recognize a condition unrelated to the outcome). Overall, 159 consecutive patients were enrolled. Type 1 errors were 5% in Group A, 4% in Group B and 9% in Group C. Type 2 errors were 18% in Group A, 34% in Group B, and 30% in Group C. Fully correct diagnoses or Type 3 errors were present in 77% of patients in Group A, 62% of patients in Group B, and 61% of patients in Group C. Clinical errors of any type were not related with the LOS in the ICU or in the hospital, age and the number of underlying chronic diseases.