We describe a patient with insulin-dependent diabetes mellitus who noticed pain and stiffness in the neck and painful spasms and rigidity of the right thigh. Continuous motor unit activity was recorded in the lower limb muscles on the right side and in the cervical paraspinal muscles. Cutaneomuscular reflexes were at an abnormally low threshold recording from the muscles of the right leg. Laboratory investigation revealed anti-GAD antibodies in serum and oligoclonal bands in the cerebrospinal fluid. We conclude that the patient has atypical stiff-person syndrome.