Objective. To estimate the incidence and characteristics of adverse events (AEs) and no-harm events (NHEs) in critically ill patients. Design. Observational, prospective, 24-h cross-sectional study with self-reporting. Setting. Seventy-nine intensive care units at 76 hospitals. Measurements. Number of events, risk of AEs and NHEs, types of incidents, severity and avoidability of incidents. Results. A total of 1017 patients were included in the study; 591 (58%) were affected by one or more

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... nts. Of the 1424 valid incidents, 943 (66%) were NHEs and 481 (34%) were AEs. The individual risk of suffering at least one incident was 62%, at least one NHE 45% and at least one AE 29%. The median number of incidents, NHEs and AEs was 6, 3 and 2 per 100 patient-hours, respectively. Seventy-four per cent of the incidents were related to medication (24%), equipment (15%), nursing care (14%), accidental withdrawal of vascular accesses and catheters (10%) or airways and mechanical ventilation (10%). AEs resulted in temporary damage in 29% and in permanent damage or damage that compromised patients' lives or contributed to their death in 4%. Incidents were avoidable in 79% of cases (90% in NHEs and 60% in AEs, P , 0.05). Conclusions. The individual risk for incidents in critical patients is high. Many incidents did not harm patients, some caused damage and a few were related to the patient's death. Most incidents were considered avoidable.