Of 95 new cases of parkinsonism referred to a department of geriatric medicine, 48 (51%) were associated with prescribed drugs. Clinical features in drug-induced and idiopathic cases were very similar, including the proportion with typical tremor. 25% of patients with drug-induced parkinsonism (DIP) could not walk when first seen and 45% required hospital admission (for a median stay of 23 days, range 5-101). The clinical features of DIP resolved permanently in two-thirds of cases in a mean of 7 weeks but with a range of 1 to 36 weeks. 5 cases of DIP initially resolved but idiopathic parkinsonism developed after an interval of 3 to 18 months. Perhaps some old people have low striatal dopamine levels and a small neuroleptic effect tips them into overt parkinsonism or unmasks latent idiopathic disease. The commonest offending drug was prochlorperazine (21 cases). In no case did this drug seem to be indicated.