Hereditary inclusion body myopathies are a clinically heterogeneous group of disorders characterized by adult-onset, slowly progressive muscle weakness and typical histopathology: rimmed vacuoles and filamentous inclusions. The disorders are usually inherited as an autosomal recessive trait. The gene responsible for the disease found in Iranian Jews, who present with quadriceps-sparing myopathy, maps to chromosome 9p1-q1. We address the question of whether hereditary inclusion myopathies are genetically as well as clinically heterogeneous disorders. We mapped the disease gene segregating in two families of Afghani-Jewish and one family of Iraqi-Jewish descent to the chromosome 9 locus. Similarly, the disease gene segregating in a non-Jewish family from India mapped to the same locus. By contrast, the disease gene segregating in a French-Canadian family in which affected individuals had central nervous system involvement as well as hereditary inclusion body myopathy, did not map to this locus. We conclude that many but not all forms of autosomal recessive hereditary inclusion body myopathy are caused by a gene defect that maps to chromosome 9p1-q1.