A six year old boy had congenital hypotonia and nonprogressive proximal muscular weakness, with mild abnormalities in the E. M. G. and normal serum enzyme levels. There was lack of fibre type differentiation in the quadriceps muscle biopsy. The fibres had high oxidative enzyme activity and low ATPase 9.4 activity. In almost every fibre there were multiple areas of focal decrease of oxidative enzyme activity, resembling in few of them the lesion described in Central Core Disease. There was abscence of mitochondria and disorganization of the sarcomere with streaming of the Z line within the lesions. The clinical and histological observations have close similarity to the cases first described by A. G. Engel et al. in 1971 as "Multicore Diseases" and to other similar reported cases.