Antiepileptic drug intoxication: factors and their significance. A retrospective chart review (1979-1985) was performed to identify probable causes of intoxication with antiepileptic drugs (AEDs). We identified 141 patients meeting clinical and laboratory criteria for intoxication and 17 with clinical signs but with serum concentrations within the therapeutic range. The majority were epileptic patients; almost half were treated with monotherapy, most with phenytoin (PHT). The causes of intoxication in the epileptic patients were iatrogenic (41%), inappropriate dose self-adjustment (34%), suicide attempt (18%), inappropriate caretaker dose adjustment (9%), accidental ingestion (8%), unrecognized drug interaction (6%), and association with intercurrent illness (2%). Twenty-two patients had more than one probable cause of intoxication. In nonepileptic patients the causes were suicide attempt (50%), accidental ingestion (27%), and iatrogenic (23%). Most patients had signs of ocularmotor and vestibulocerebellar dysfunction. Rarely described manifestations of intoxication, such as seizures or choreoathethosis, were observed in a few patients. The average hospital stay was 6.9 days; there was no mortality, and all patients recovered fully. We conclude that AED intoxication is a major but preventable cause of morbidity and that suicide attempts are an important and underrecognized contributor in both epileptic and non-epileptic patients. 