BACKGROUND: Botulinum toxin type A (BTX-A) is widely used for facial esthetics but is incompletely studied. OBJECTIVE: This study was conducted to evaluate the efficacy and safety of BTX-A treatment of glabellar lines. METHODS: Patients with moderate to severe glabellar lines at maximum frown received intramuscular injections of 20 U BTX-A (BOTOX, Allergan, Inc, Irvine, Calif) or placebo into 5 glabellar sites. Patients were followed up for 120 days after injection. Outcome measures were physician rating of glabellar line severity at maximum frown and rest, patient assessment of improvement, and vital sign and adverse event monitoring. RESULTS: Two hundred sixty-four patients were enrolled (BTX-A: 203, placebo: 61). There was a significantly greater reduction in glabellar line severity with BTX-A than with placebo (all measures, every follow-up visit; P <.022). The effect was maintained for many patients through day 120. There was a low occurrence (5.4%) of mostly mild blepharoptosis in the BTX-A group. CONCLUSION: BTX-A injections are safe and effective in reducing the severity of glabellar lines.