Complications of medical therapy requiring hospitalization affect the costs and quality of medical care. We studied all admissions to the medical services of a public teaching hospital to characterize current incidence and cause of iatrogenic admissions. We studied 834 admissions resulting in 47 distinct iatrogenic events and 45 iatrogenic admissions (5.4%). Thirty-five cases were caused by medications, nine by procedures, one by radiotherapy, one by transfusional therapy, and one by nosocomial infection. Almost 50% of these admissions were avoidable. Though the incidence of iatrogenic admissions in this study is similar to that in previous reports, the profile of the responsible agents is different. We did not find relationships with age, number or type of diagnoses, or number of medications on admission. Study of other patient and physician characteristics may be more rewarding in reducing the number of iatrogenic complications.