The clinical findings in six patients from three families with 4-hydroxybutyric aciduria are described. The onset of disease was in early infancy in all cases. All infants presented with severe global delay and severe hypotonia, and all patients had seizure disorder. Eye findings included optic atrophy in two patients, and retinitis pigmentosa in one. Three patients had choreoathetosis, two had myoclonus and one had severe dystonia. The urine 4-hydroxybutyric acid was 300-1000 times that of normal, and other organic acids related to its further metabolism or to its inhibitory effect on beta-oxidation were also increased. The administration of vigabatrine rapidly reduced the excretion of 4-hydroxybutyric acid promptly, and in the long-term its excretion could be kept at 80-200 times that of normal. However, the clinical course of the disease improved in only two, remained the same in two, and worsened in the remaining two patients.