Forty-one patients with hemifacial spasm received botulinum A toxin in total 73 visits. In 68 of 73 visits(93%), substantial improvement with peak effect(change in severity of hemifacial spasm 22 ) was obtained, with a mean total dose of 12.5 units. Mean severity of hemifacial spasm before and after treatrnent were 3.8 and 1.1 respectively on a 0-5 scale. Mean muscle dose of orbicularis oculi was 9.0 units There was a significant association between muscle dose and post-treatment weakness of orbicularis oculi(Spearman correlation coefficient, 0.42691). There was also a striking and significant association between post-treatment weakness of orbicularis oculi and peak effect(Spearman correlation coefficient, 0.74883). Lagophthalmos occurred only in 2 of 28 visits (7%) who received lesser than 10.0 units for orbicularis oculi as compard to 22% in the higher dose group. But peak effects showed no significant difference between the two groups(p =O.I30). We suggest that the occurrence of lagophthalmos can be reduced with the dose lesser than 10.0 units for orbicularis oculi, maintaining the significant effect.