OBJECTIVE: This study evaluates the efficacy of botulinum toxin A injections used in conjunction with physical therapy for the treatment of piriformis syndrome. DESIGN: This a double-blind, placebo controlled clinical trial using electrophysiologic criteria for patient selection and a visual analog scale to assess treatment efficacy in relieving pain. RESULTS: As measured on the visual analog scale, patients injected with botulinum toxin A experienced more relief from pain than patients receiving lidocaine with steroid (P < 0.05) and more relief than patients receiving placebo (P = 0.001). CONCLUSIONS: Injection with botulinum toxin A is an effective adjunct to physical therapy in the treatment of piriformis syndrome. H-reflex prolongation by flexion, adduction, and internal rotation (FAIR test) beyond 1.86 msec (3 SD) of the mean is a clinical indication of piriformis syndrome.