Ten cases of oculopharyngeal muscular dystrophy (OPMD) were examined ultrastructurally. Two very different types of filamentous inclusions were observed: (1) Nuclear inclusions composed of 8.5 nm external diameter tubular filaments organized in palisades and similar to those described by Tomé and Fardeau (1980). They have not yet been reported in other muscle diseases. Their presence in 100% of our cases confirms they are the morphological hallmark of OPMD. (2) 16-18 nm external diameter tubular filaments. These were similar to the inclusions observed in inclusion body myositis (IBM) and morphologically very different from the first type. They were randomly dispersed or arranged in bundles near cytoplasmic debris and whorls of membranes. They were found in cytoplasm. Only once were they observed in a nucleus. These inclusions have been described in IBM but also in other diseases. They were found in 80% of our OPMD cases.