The muscle findings in a patient with acromegaly of 20 years duration are presented. The patient demonstrated mild muscular weakness and atrophy. Standard needle electromyography was normal and single fiber electromyography showed normal motor unit densities. Muscle biopsy revealed normal size type-I muscle fibers, but three populations of type-II fibers - hypertrophied, atrophied, and normal-sized fibers. Hypertrophy of type-II fibers may be the direct result of the excess growth hormone, while the atrophic fibers may result from the disturbance of other endocrine function.