All patients admitted during a 33-month period to a multidisciplinary intensive care unit were prospectively studied in order to determine the incidence and severity of drug-induced illness leading to the admission. The role of underlying diseases was assessed and the avoidability of drug-induced illness considered. Out of 1651 patients, 97 (5.88%) were admitted because of drug-induced illness; 74 of these had serious underlying diseases. 13 (13.4%) of the 97 patients died, but underlying diseases accounted for 4 of the 13 fatalities. In nearly half of the cases, the drug-induced illness appeared potentially avoidable.