We describe a slowly progressive myopathy with unique crystalloid inclusions in type 2 muscle fibers in a father and his son, as well as one more unrelated individual. The inclusions were strongly eosinophilic and purple by the Gomori method. They were composed of vesicular profiles, approximately 20 nm in cross-diameter, connected by radially arranged double spokes arising at 60 degrees angles. The inclusions were not related to any normal cellular organelle. Extensive immunohistochemical studies failed to reveal their chemical nature. It is suggested that this is a new congenital myopathy with characteristic intracytoplasmic inclusions, occurring sporadically or with an autosomal dominant pattern of inheritance.