Oculopharyngeal muscular dystrophy (OPMD) is usually a late onset, autosomal dominant dystrophy that affects extraocular eye muscles, pharyngeal muscles, and the trunk and limb musculature. In the present presumably recessively inherited case, with a clinical history of oculopharyngeal myopathy and distal weakness, paracrystalline mitochondrial inclusions and unique nuclear inclusions were found. In a biopsy obtained from the erector spinae muscle, marked muscle fibre atrophy and hypertrophy, occasional muscle fibre necrosis, and considerable fibrosis of the endomysium were noted. Similar signs of a chronic myopathy could already be detected in a biopsy from the anterior tibial muscle that had been obtained 10 years before. In both muscles, nuclear inclusions were seen in numerous severely affected, atrophic muscle fibres. These inclusions consisted of straight or helically wound 2-4 nm filaments. The outer diameter of the double helix was 12-15 nm and the periodicity of its repeats was about 15 nm. The filaments were often accumulated in clusters with a paracrystalline arrangement. No nuclear inclusions consisting of 8.5 nm tubular filaments, typically found in cases of OPMD, were detected. In addition, paracrystalline inclusions were present in a large number of mitochondria in several muscle fibres of the erector spinae muscle indicating that mitochondria could be primarily involved in the disease.