Mutations in the lamin A/C gene have been reported in a variety of disorders including autosomal dominant Emery-Dreifuss muscular dystrophy and autosomal dominant limb girdle muscular dystrophy with cardiac conduction block or limb girdle muscular dystrophy type 1B (LGMD1B). However, how these mutations are involved in developing these diseases is not known. We examined morphological changes of the skeletal muscle in two cases of LGMD1B in a family, directing our attention to the nuclear envelope and its underlying structures where lamin A/C is located. Although conventional fluorescence microscope revealed no discernible abnormality in the distribution of emerin and lamin A/C, a serial multi-layer scanning with confocal laser scanning microscope showed an attenuated and uneven distribution of lamin A/C. Furthermore, under an electron microscope, the nuclear fibrous lamina and inner nuclear membrane were relatively indistinct compared to controls. These changes in the myonuclei may be related to pathomechanisms of the present cases.