The epidemiology of neuromuscular diseases was studied in the county of Orebro, Sweden (study population 270,000). Several different sources of data were utilized, compared and validated. On the prevalence of day (January 1, 1988) 474 patients were identified. The rate per 100,000 population was 92 for the postpolio sequelae (PPS) and 84 for the other neuromuscular diseases (motor neuron disease 9, hereditary neuropathies 9, myoneural disorders 16, myotonic disorders 19, muscular dystrophies 20 and myositis 11). Of the patients with the PPS, 80% reported late-onset symptoms. On the basis of an expanded survey including all medical records in one health care district, the prevalence of the PPS was estimated to be 186/100,000 population.