Abstract A muscle biopsy performed on a 16-year-old boy with progressive myopathy revealed hitherto unrecognized peculiar inclusions which consisted of 3 types of structures. The first type consisted of laminated tubulomembranous structures and most of the inclusions belonged to this type. The lamellae were regularly spaced with a periodicity of 8.5–9 nm and curving a little, and were observed as concentric lamellae according to the plane of sectioning. The second type of inclusions consisted of curvifilamentous material. The third type had the appearance of moderately electron-dense granular material surrounded by a single unit membrane. The origin and nature of these inclusions is obscure, but the diagnosis of some kind of storage myopathy was suspected in this case.