The objective of this study was to determine whether the continuous intrathecal delivery of baclofen will control spastic hypertonia associated with long-standing hemiplegia from acquired brain injury. Six hemiparetic patients (average age, 50 (range, 42-66) yr) with more than 6 mo of disabling lower limb spastic hypertonia on one side caused by either a unilateral traumatic brain injury or a stroke were recruited in a consecutive manner. The setting was a tertiary care outpatient and inpatient rehabilitation center directly attached to a university hospital. Patients were screened via a randomized, double-blind, placebo-controlled, crossover design to receive either an intrathecally administered bolus injection of normal saline or 50 μg of baclofen. Data for Ashworth rigidity scores, spasm scores, and deep tendon reflex scores were collected on the affected upper limb and lower limb side. Those who dropped an average of two points on their affected lower limb side Ashworth scores were then offered computer-controlled pump implantation for continuous intrathecal administration of baclofen. Differences over time were assessed via descriptive statistics and Wilcoxon's signed-rank test. After 3 mo of treatment, the average lower limb Ashworth score on the affected side decreased from 3.7 ± 1.0 to 1.9 ± 0.6 standard deviation (SD) (P < 0.0001), the reflex score from 1.8 ± 1.3 to 0.5 ± 0.8 SD (P = 0.0208), and the spasm score from 1.3 ± 1.2 to 0.8 ± 1.3 SD (P > 0.05). The average upper limb Ashworth score on the affected side decreased from 3.4 ± 0.9 to 2.1 ± 0.9 SD (P = 0.0002), the reflex score from 2.3 ± 0.5 to 1.7 ± 0.5 SD (P > 0.050, and the spasm score from 0.8 ± 1.3 to 0 ± 0 SD (P > 0.05). The average intrathecally administered dose of baclofen that was required to attain these effects was 205.3 μg, which was continuously infused for 24 h. Continuous intrathecal infusion of baclofen is capable of maintaining a reduction in the dystonia on the hemiparetic side without significantly affecting motor strength on the normal side.