Objective: Assessment of the effectiveness of constraint-induced (CI) movement therapy and quantitative evaluation of the effects of CI therapy. Design: Intervention study; case series; pretreatment to posttreatment measures and follow-up 3 months after intervention. Setting: An outpatient department. Patients: Five chronic stroke patients with moderate motor deficit; convenience sample. Interventions: CI therapy consisting of restraint of the unaffected upper extremity in a sling for 14 days combined with 6 hours of training per weekday of the affected upper extremity. Main Outcome Measures: Actual Amount of Use Test (AAUT), Motor Activity Log (MAL), Wolf Motor Function Test (WMFT), and Arm Motor Ability Test (AMAT) Results: There was a substantial improvement in the performance times of the laboratory tests (AMAT, WMFT, p ≤ .039) and in the quality of movement (AMAT, WMFT, p ≤ .049; MAL, p = .049), particularly in the use of the extremity in 'real world' environments (AAUT, p = .020), supported by results of quantitative evaluation. The effect sizes were large and comparable to those found in previous studies of CI therapy. Conclusions: CI therapy is an efficacious treatment for chronic stroke patients, especially in terms of real world outcome.