Botox Cosmetic (Botox) is a formulation of the neuromuscular blocking agent botulinum toxin type A (BTX-A). When injected into hyperactive corrugator superciliaris and/or procerus muscles of the face that predominantly control frowning, Botox produces a transient (3- to 6-month), dose-dependent localized muscle weakness, resulting in a temporary improvement in glabellar frown lines ('brow furrows'). After a decade of successful 'off-label' use, the efficacy and tolerability of Botox (total dose 20 biological units) in the treatment of glabellar frown lines have been demonstrated in two identical, large, multicenter, randomized, double-blind, placebo-controlled pivotal trials in a total of 537 subjects, mostly women, with moderate or severe glabellar lines during facial animation. Based both on subjects' and physicians' assessments, the improvement in glabellar lines with Botox was superior to that with placebo at each visit during the 120-day post-injection follow-up period, beginning on day 7 post-injection. The peak effect was seen on day 30 post-injection when 80% of subjects in the two studies combined had the severity of their lines at maximum frown reduced to mild or none, as assessed by their physician, and 89% had at least a moderate (> or =50%) improvement in the appearance of their glabellar lines, as rated by themselves. In a noncomparative extension of these trials, there was a tendency for a higher proportion of subjects to respond to Botox injections after a second and third treatment session. Botox injections for glabellar lines are well tolerated. Headache, the most common adverse event, occurred with a similar frequency to placebo in the two pivotal studies (13% vs 18%). Temporary blepharoptosis occurred in 3.2% of Botox recipients; however, the incidence of this adverse event tended to decrease with repeated treatment sessions. In summary, Botox injections offer a convenient, effective, and well tolerated treatment for improving glabellar frown lines. Repeated injections are necessary to maintain a long-term effect; however, this technique clearly represents an attractive option for individuals who wish to avoid a more major procedure.