To determine the pattern of and the risk factors for adverse drug reactions (ADRs) in Hong Kong, a prospective study of acute admissions to 2 general medical wards at the Prince of Wales Hospital was undertaken. Of the 1701 admissions included in this study, 74 (4.4%) were attributed to ADRs. Sulphonylureas, nonsteroidal anti-inflammatories (NSAIDs) and insulin accounted for 61% of cases. The most frequent ADRs were hypoglycaemia (43%) and gastrointestinal haemorrhage (29.7%). Both old age and impaired renal function appear to be important risk factors for ADRs. In such situations, careful dose adjustments, use of an alternative drug or total avoidance may be necessary. Particular attention should be given to oral hypoglycaemic drugs and NSAIDs.