A retrospective epidemiological survey of the principal neuromuscular disorders was undertaken in the population under the age of 20 yr in Bologna city and province. The incidence of Duchenne muscular dystrophy (DMD) proved to be 25.8 x 10(-5), that is, comparable with the outcome of neonatal screening studies. The incidence of spinal muscular atrophy (SMA) was very high (11.2 x 10(-5), probably the result of our greater awareness and recognition of this disorder. The prevalence of neuromuscular disorders in the 0-19 yr population is 1.5 times that in the general population; that of DMD is 28 x 10(-5) vs 6.3 x 10(-5) and that of the SMA 6.5 x 10(-5) vs 1.2 x 10(-5). Our results indicate that neuromuscular disorders, particularly DMD and SMA I and II, have a much higher prevalence in the first two decades of life than is generally thought. Awareness of the higher prevalence of neuromuscular disorders among the under-20s is essential to the adequate planning of medical services.