Penicillamine is known to be effective therapy for Wilson's disease. However, the clinical consequences of the abrupt and permanent withdrawal of penicillamine have not been investigated. We studied 11 patients who stopped their own treatment after having been treated successfully with penicillamine (1 to 2 g per day) for periods of 3 to 19 years. Eight died of hepatic decompensation or fulminant hepatitis after an average survival of only 2.6 years. In another 13 patients, penicillamine was discontinued by the physician because of serious adverse reactions. In these patients, penicillamine was replaced with trientine (1 to 1.5 g per day), a newer chelating agent. All but one of these patients (who was killed accidentally) are alive at this writing, from 2 to 15 years later. Our observations suggest that discontinuation of penicillamine in patients with Wilson's disease results in rapid clinical deterioration, which is often fatal. The replacement of penicillamine with trientine appears to prevent this adverse clinical course.