A comprehensive study of inherited neuromuscular disease was carried out in Northern Ireland between 1 February 1993 and 30 June 1994. Cases were ascertained from eight different sources and investigations and diagnoses were reviewed. Five hundred and forty three individuals were identified giving an overall prevalence of inherited neuromuscular disease of 1 in 2900 of the population. The prevalence of myotonic dystrophy was higher than that in most previously reported studies and accounted for 25% of all cases. Congenital myopathies were also found more frequently than expected. The overall prevalence compares well with that estimated by Emery from the reported prevalence rates of individual diseases.