OBJECTIVE: To determine the incidence, risk factors, severity, and preventability of iatrogenic events (IEs) as a cause of intensive care unit (ICU) admission. DESIGN: Comparison of patients admitted or not for IE. IE was diagnosed after assessing independently predefined criteria. SETTING: The ICU of a teaching hospital. PATIENTS: All patients consecutively admitted over 6 months. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: Characteristics of patients, supportive treatments, length of stay, and outcomes were recorded. For patients admitted for IE, cause, origin, and preventability of IE were assessed by consensus. Of 528 patients, 103 (19.5%) were admitted for IE. Their Simplified Acute Physiology Score (SAPS) II was higher (41.2 +/- 22.6 versus 31.4 +/- 18.6), as was their Logistic Organ Dysfunction (LOD) score. Surgical admissions and admission for shock were more frequent. The main risk factors were age, underlying disease, low Mac Cabe or Knaus score, number of physicians treating the patient, number of drugs prescribed, and other hospitalization within 1 month. Length of stay was higher (11.1 days versus 7.9 days, 0.5-6.0, p = 0.02). Catecholamine drugs, blood transfusion, and parenteral nutrition were more frequently required in the IE group. ICU mortality was 15.5% in the IE group and 11.3% in the group without IEs [not significant (ns) after adjustment]. IE was considered as probably preventable in 73.8% of cases. CONCLUSION: Of admissions to the ICU, 19.5% resulted from IE, with high proportion of shock, leading to greater need for invasive treatments and longer stay in the ICU. Most cases of IE seemed preventable.