OBJECTIVES: To evaluate the impact of intrathecal baclofen (ITB) on function and quality of life (QOL) and to obtain efficacy and safety data in poststroke spastic hypertonia. DESIGN: Prospective open-label multicenter trial with follow-up at 3 and 12 months. SETTING: Twenty-four stroke treatment centers in the United States. PARTICIPANTS: Ninety-four stroke participants (age range, 24-82 y) with spastic hypertonia. Seventy-four participants underwent ITB pump implantation. INTERVENTION: Participants were implanted with an ITB pump. MAIN OUTCOME MEASURES: FIM instrument and QOL (Sickness Impact Profile [SIP]) changes, spastic hypertonia (Ashworth Scale), and safety. RESULTS: FIM scores improved overall in repeated-measures analysis of variance (ANOVA) (P = .005) and by 3.00 +/- 7.69 (P = .001) at 3 months and by 2.86 +/- 10.13 (P = .017) at 12 months. Significant improvements in SIP scores were noted overall (repeated-measures ANOVA, P < .001) and at 3 (P = .003) and 12 months (P < .001). The combined average Ashworth Scale score of the upper and lower limbs decreased by 1.27 +/- 0.76 (P < .001) at 3 months and by 1.39 +/- 0.73 (P < .001) at 12 months from baseline, which was significant overall (repeated-measures ANOVA, P<.001). Strength in the unaffected side did not change overall (repeated-measures ANOVA, P = .321) or at either 3 (P = .553) or 12 months (P = .462). Minimal adverse events and device complications were reported. CONCLUSIONS: There was significant improvement in function, QOL, and spastic hypertonia at 3 and 12 months after implant, without adversely affecting muscle strength of the unaffected limbs. Data suggest that ITB therapy is a safe and efficacious treatment for spastic hypertonia resulting from stroke.