Following several months of low back pain, a 36-year-old man developed progressive stiffness of the abdominal, low back, and thigh muscles. On examination, these muscles demonstrated marked hypertonia consistent with the clinical diagnosis of stiff-person syndrome. The patient demonstrated increased lumbar lordosis and had focal hyperhidrosis at different sites. Electromyography showed continuous activity of the paraspinal and thigh muscles, and serum and cerebrospinal fluid antibodies to glutamic acid decarboxylase (GAD) were markedly elevated. Diazepam and Lioresal offered partial pain relief. Paraspinal muscle administration of botulinum toxin A reduced the tone of paraspinal and thigh muscles significantly and resulted in marked improvement of ambulation and cessation of pain.