The prevalence of hereditary motor and sensory neuropathies (HMSN) and their distribution according to the severity of the disability were studied in a population-based series of Swedish children 2-15 years old. The prevalence per 100 000 of total peroneal muscle atrophies was 21.6 and of all clinical HMSN 19.0 Among HMSN, de- and remyelinating types (HMSN I) constituted 8 per 100000 and neuronal-axonal types (HMSN II) 11. Eighteen of the 21 HMSN I cases and 26 of the 29 HMSN II were considered to represent an autosomal dominant mode of inheritance. Ten per cent of all children were severely, 70% moderately and 20% mildly disabled. All the severely affected children belonged to the HMSN I group and 9 of the 10 mildly affected to HMSN II.