Studies utilizing single doses of scopolamine have suggested a role for the cholinergic system in memory. Results are consistent in identifying a selective effect on the early encoding stage of information processing. In terms of long-term administration of anticholinergics, patients with Parkinson's disease often display memory deficits. However, underlying pathology within the forebrain cholinergic system complicates the study of treatment effects in this disorder. We therefore assessed multiple memory routines in 20 cognitively intact patients with dystonia where no such pathology has been identified. Patients were tested before and after 2–4 months of 15–74 mg of trihexyphenidyl daily. Twelve tolerated this regime. Compared to control subjects, matched for age and I.Q., only tests with a single presentation of the material to be remembered were affected at follow-up. The speed of information processing was also significantly reduced. Age was strongly related to memory performance in the patient group alone and interacted with dose and duration of treatment. Results suggest that drug-induced slowing of mentation was responsible for impaired encoding, particularly in older patients. These findings affect treatment strategies, especially now that injections of botulinum toxin have proved to be highly effective for certain forms of focal dystonia.