Oxybutynin has been widely prescribed in the United Kingdom for more than 5 years on a named patient basis. Complete knowledge of its side effects is therefore particularly important. The literature contains remarkably little data on this topic. We therefore reviewed 192 consecutive patients for whom the drug had been prescribed in a district general hospital; 57% derived benefit while 76% noted side effects, none of which was dangerous or irreversible. Oxybutynin obtained from the two principal suppliers did not appear to differ either in efficacy or side effects. We discuss the uncertain medicolegal implications of named patient prescriptions.