The prevalence of child neuromuscular disease in Southern Norway by January 1st, 1983, was studied by collecting data from all available sources. All children born 1. 1. 1965 or later were included in the study. The total group consisted of 110 patients from 17 different diagnostic categories. Total prevalence on this group was found to be 24.9 X 10(5). Duchenne muscular dystrophy (DMD), with a prevalence of 10.89 X 10(5) constituted 29.2% of the total material. In the spinal muscle atrophy group (SMA), we found a significant increase in the number of boys affected, although an autosomal recessive mode of inheritance was found likely in all probands. Prevalence figures of child neuromuscular disease are hard to compare, as most studies deal with an adult population. The prevalences of common and well-known large categories of neuromuscular diseases in childhood are in agreement with previous studies. For less well known and mild diseases, our figures are low. This may be due in part to a later onset and in part to a health system not sensitive to parents' complaints.