• Three patients had nonprogressive congenital neuromuscular disease with uniform type 1 fiber. Uniform fiber type was defined as more than 99% of muscle fibers belonging to one type. These cases were characterized by early onset of symptoms, mild proximal weakness, hyporeflexia or areflexia, normal serum muscle enzyme levels, short duration of motor unit potentials, uniform type 1 fibers, and nonprogression. These cases represent a distinct form of nonprogressive congenital neuromuscular disease.