Spasticity can affect individuals with spinal injury, spinal disease, or multiple sclerosis. In most cases, spasticity is useful because it helps compensate for motor deficits. Oral medication is ineffective or produces intolerable side effects in ≅ 30% of patients with severe spasticity and surgeries can sometimes have effects inappropriate for patients requiring some degree of spasticity for function. Unsuccessful treatment of severe spasticity affects physical, social, and emotional functioning, as well as nursing care and overall cost of treatment. Intrathecal baclofen, a potent inhibitor of spinal synaptic reflexes, reduces both spasticity and spasms, thus leading to improvements in functioning and patient perception of quality of life, as well as ease of caretaking. Intrathecal baclofen can produce minimal side effects. The programmable pump allows precise dose titration that can be adjusted over a 24-h period for maximum effectiveness. Intrathecal baclofen generally remains effective for years without producing drug tolerance. Although complications are relatively uncommon, most involve mechanical compromise of the catheter. Cost analysis shows that there is an overall savings associated with intrathecal baclofen therapy, primarily due to a reduction in required hospitalizations and medical care for conditions resulting from spasticity. Intrathecal baclofen is a safe, efficacious, titratable, reversible, and cost-effective treatment for severe spinal origin spasticity, including spinal cord injury, spinal cord disease, and multiple sclerosis.