Of 1998 patients consecutively admitted to Geriatric Medicine Departments in England, Wales and Scotland in 1975–6, 81.3% were receiving prescribed drugs at time of admission. Adverse reactions were noted in 248 patients, representing 15.3% of prescribed drug takers. In 209 of these patients, it was thought that an adverse reaction had contributed to the need for admission to hospital. Full recovery from adverse reactions and sequelae occurred in 68% of those with such reactions. Hypotensive drugs, antiparkinsonian drugs and psychotropics carried the greatest risk of adverse reactions although the largest single number of adverse reactions (60) were due to diuretics which were by far the most commonly prescribed drugs (37.4% of sample).