• Three quantitative measures of autonomic nervous system (ANS) function were evaluated in 12 patients with two types of autosomal dominant neuromuscular disorder, type 1 hereditary motorsensory neuropathy and myotonic dystrophy. The three measures were latency of the pupillary light reflex, dark-adapted pupil size during parasympathetic blockade, and ECG RR interval variation. The results showed deficits in sympathetic and/or parasympathetic nervous system function in several patients, with a variability of expression expected in autosomal dominant genetic diseases. The ANS function may commonly be deficient in both of these disorders. Further investigation is required to determine the potential clinical importance of these findings.