Congenital muscle fiber type disproportion (CFTD) has been described as a form of congenital myopathy characterized by the smallness and marked predominance of type 1 fibers in a muscle biopsy. Clinical manifestations include hypotonia, nonprogressive muscle weakness, joint contractures, and skeletal deformities. However, it has also been noted that the same pathologic alterations appeared in clinically diverse conditions. Recently, we experienced a family, a mother and two children, in which a muscle biopsy showed the mother to have muscle fiber type disproportion. This case was unusual in that there was a significant progression of weakness, an absence of neonatal hypotonia, and other commonly associated musculo-skeletal deformities. In this report, we describe the clinicopathologic features of the family with a brief review about muscle fiber type disproportion.