A patient with thioridazine-hydrochloride-associated agranulocytosis is described and eight previously reported cases are reviewed. This complication is most likely due to a direct toxic effect on the bone marrow. As in our case, markers for an immunologically mediated mechanism have not been found. Thioridazine-hydrochloride-associated agranulocytosis usually occurs between the fifth and 11th week of therapy and is not related to the total dose of drug received. Three of the nine patients with thioridazine-hydrochloride-associated agranulocytosis have died from infectious complications. Thus, careful monitoring for infection and prompt therapy are indicated.