Compliance with anticonvulsant therapy was assessed in 95 epileptic subjects with uncontrolled seizures. Following a seizure for which an ambulance was called, patients were interviewed and questioned on their medication taking. Compliance was also determined from measurement of anticonvulsant concentrations in saliva, and from intervals between collection of drugs from pharmacy. Compliance failure was found to be instrumental in precipitating 29 (31%) of seizures for which the ambulance was called. At the time of interview, 35 (37%) subjects were not taking their medication regularly in accordance with prescribing instructions. In addition to forgetting medication, many subjects deliberately stopped or changed doses of drugs. Other causes of non-compliance which were indentified included patient misunderstanding of prescribing instructions. Compliance with therapy was positively related to perceived benefit from anticonvulsant therapy.