We report two families with a disorder, probably autosomal recessive, characterized by tremor of juvenile onset, dystonia, and myoclonus with preserved cognitive, cerebellar, and peripheral nervous system functions. During 4 years' follow-up, mild spasticity appeared. Magnetic resonance imaging (MRI) revealed mild diffuse changes in the white matter. Central conduction times for visual, motor, and sensory systems were all prolonged. Extensive metabolic work-up failed to reveal lysosomal, peroxisomal, mitochondrial, or other metabolic abnormalities.