Eight unrelated children with centronuclear (myotubular) myopathy are described, ranging in age at the time of diagnosis from 5 days to 12 years. Six had an intrauterine onset and 5 were severely asphyxiated at birth. All had facial involvement and 6 had ophthalmoplegia. Detailed study of the parents in 7 of the families suggested an autosomal recessive inheritance or sporadic occurrence in 2 and X-linked inheritance in 5. Classification in this very variable disorder should be based on severity and mode of presentation together with the genetic pattern, allowing three subgroups to be defined: a severe neonatal X-linked recessive type, a less severe infantile or juvenile autosomal recessive type and a milder autosomal dominant type. For genetic counselling, available relatives should be examined for mild degrees of clinical involvement and morphological abnormalities on needle muscle biopsy.