Two hundred and fifty patients with hemifacial spasm from the Movement Disorder Clinic, at Siriraj Hospital have been treated with botulinum toxin injection since January 1989 as a collaborating research project with Smith-Kettlewell Eye Research Institute in San Francisco. Each patient received 30 units in four injection sites over the hyperkinetic facial muscles. There were 169 female and 81 male patients, the sex ratio of female to male was 2.1:1. The mean age of all patients was 50.2 +/- 12.6 years with the range of 22 to 78 years. The majority of patients had been suffering for 3-10 years. The results of botulinum toxin injection were classified as excellent in 81.2 per cent, moderate improvement 10.0 per cent, mild improvement 6.8 per cent and no improvement or worse in 2.0 per cent. There were complications of mild transient facial weakness in 44 patients (17.6%) mild ptosis in 7 patients (2.8%) and excessive lacrimation in 1 patient (0.4%). The effect of botulinum toxin treatment lasted for 3-6 months duration. Botulinum toxin injection is a simple and effective out-patient treatment for patients with hemifacial spasm with no systemic side effects and minor transient local complications.