A 21 year-old boy suffered from a congenital myopathy with predominantly proximal distribution and mild involvement of facial and oculomotor muscles. A third muscle biopsy at age 20 and a reappraisal of two previous biopsies led to the diagnosis of centronuclear myopathy. A review of about one hundred cases in the literature shows that age of onset, mode of inheritance and pathologic features may differ in large proportions. For genetic counselling investigations were performed on the patient's parents, brother and sister. All family members were clinically normal. Electromyography showed short potentials suggestive of myopathy in both parents but much more so in the patient's sister. Biopsies revealed equivocal changes, especially in mother and sister. No definitive conclusions about the mode of inheritance could be drawn in this family.