Nemaline myopathy belongs to the group of congenital non-progressive myopathies; however, in rare cases death occurs in early infancy. We report two cases of rapidly fatal nemaline myopathy. The first patient, who died at the age of 26 months, showed atrophy of type 1 fibers containing numerous rods in biopsy sections. Biopsy of the second patient, who had died at the age of 5 months, revealed severe maturational arrest and myopathy, but rods were so rare that diagnosis could only be made at the ultrastructural level. Autopsy of both patients showed that atrophy of type 1 fibers and maturational arrest had disappeared in the very same muscles; rods had moved to a central position in the first and significantly increased in number in the second case. Diaphragma muscles contained abundant amounts of rods in both cases. The cardiac musculature showed a few rods only in the first patient, who had developed heart insufficiency 11 months prior to death. Immunohistochemical analysis showed that rods did not contain desmin or ubiquitin.