The invention provides a pharmaceutical formulation containing tolterodine, its 5-hydroxymethyl metabolite or the racemate corresponding to tolterodine, or a pharmaceutically acceptable salt thereof, which formulation when administered to a patient provides controlled release of tolterodine, its 5-hydroxymethyl metabolite or the racemate corresponding to tolterodine, or a pharmaceutically acceptable salt thereof, such that a substantially constant serum level of the active moiety or moieties is maintained for at least 24 hours.