The relationship between Wilson's disease and epilepsy is explored, both in the literature and in a series of 200 cases of Wilson's disease. Details of 44 literature and 14 personal cases of both disorders are presented. The prevalence on December 1, 1986 of epilepsy in the Cambridge series was 6.2%, ten times higher than that of epilepsy in the general population. Seizures in Wilson's disease occur at any stage of the disease, but often begin shortly after the start of treatment. Prognosis of seizures was comparable with the best quoted figures for idiopathic epilepsy: at 7 years 60% of cases had been seizure-free for at least 5 years, and 75% for at least 2 years. Possible mechanisms of seizures are discussed. Penicillamine-induced pyridoxine deficiency is probably not involved in more than a minority of cases. It is more likely that a direct effect of copper deposition is responsible for most of the seizures.