Twelve consecutive patients with severe spasticity and hypertonia following acquired brain injury were treated with continuous intrathecal infusion of baclofen via an implanted, programmable infusion pump-catheter system for a minimum of 3 months. In every case intrathecal baclofen therapy resulted in a statistically significant reduction in upper- and lower-extremity tone, spasm frequency, and reflexes, contributing to improved functional abilities. There were no untoward side effects or complications associated with treatment. This preliminary assessment indicates that intrathecal administration of baclofen is effective in treating the disabling spasticity caused by acquired brain injury in selected patients.