Baclofen, a gamma-aminobutyric acid agonist, acts at the spinal cord level to impede the release of excitatory neurotransmitters that cause spasticity. Oral baclofen improves cerebral spasticity mildly, but its activity is limited because of its poor lipid solubility. Cerebrospinal fluid baclofen levels after intrathecal administration are many times higher than those achieved after oral administration. Continuous intrathecal baclofen infusion has been used to treat cerebral spasticity in two patient groups: in older ambulatory children with inadequate underlying leg strength, and in patients with severe spasticity in both the upper and lower extremities. Responsiveness to intrathecal baclofen is confirmed by test injections before insertion of a programmable subcutaneous pump. Continuous intrathecal baclofen infusion dosages vary from 27 to 800 micrograms/day. Continuous intrathecal baclofen infusion reduces spasticity in the upper and lower extremities, and improves upper extremity function and activities of daily living but has no effect on athetosis in the dosages used to treat spasticity. Complications related to the intrathecal catheter occur in approximately 20% of patients, and infection requiring pump removal occurs in approximately 5%. Preliminary studies indicate that continuous intrathecal baclofen infusion alleviates some forms of generalized dystonia associated with cerebral palsy.