Hypocupraemia with normal caeruloplasmin levels was found in a 21-month-old boy admitted to hospital because of repeated seizures and failure to thrive. He had blonde curly hair, spurring of the femora and tibiae, and mild anaemia, but his mental development, electroencephalogram, and structure of the hair on microscopical examination were normal. There was a general improvement in his condition with supplements of oral copper but as soon as these were reduced or stopped hypocupraemia and seizures resumed. Family investigation showed copper deficiency with mild symptoms in the mother and the maternal uncle. The pedigree suggests possible autosomal dominant or X-linked dominant transmission.