OBJECTIVES: To evaluate the clinical effectiveness of botulinum toxin (BTX) injection into the gastrocnemius muscles in patients with lumbar spinal stenosis (LSS) who have frequent nocturnal calf cramps (NCCs). DESIGN: Prospective, randomized clinical trial. SETTING: Outpatient department for interventional pain management. PARTICIPANTS: Patients (N=50) with LSS who have NCCs at least once per week were enrolled. INTERVENTION: Patients were randomly allocated to receive either conservative treatments plus gabapentin (group GPN) or BTX injection (group BTX). MAIN OUTCOME MEASURES: We assessed back/leg pain intensity, the frequency and severity of NCCs, insomnia severity, and functional disability at baseline and after 2 weeks, 1 month, and 3 months. Additionally, Patient Global Impression of Change was assessed. RESULTS: Forty-five patients completed all assessments (group GPN, n=21; group BTX, n=24). Compared with group GPN, leg pain intensity, cramp frequency, and cramp severity were significantly decreased in group BTX at all follow-up visits (all, P<.01). Also, insomnia significantly improved in group BTX at the 2-week (P=.018) and 1-month follow-up (P=.037). Functional disability significantly improved in group BTX at 2 weeks' follow-up (P=.041). At the 3-month follow-up, patients in group BTX reported a higher impression of improvement for NCC symptoms than did those in group GPN (P<.001). A mean dose of 642.8mg of gabapentin was given daily in group GPN, but 7 patients (33.3%) reported systemic side effects. There were no serious complications related to BTX use. CONCLUSIONS: BTX treatment appears to be effective and safe for NCCs in symptomatic LSS patients receiving conservative care.