Background: Alopecia areata (AA) is a T-cell-mediated autoimmune disease. Efalizumab is a T-cell-targeted therapy approved for the treatment of psoriasis. Objective: To assess the efficacy and safety of efalizumab in the treatment of moderate-to-severe AA. Methods: Sixty-two patients were enrolled into this phase II, placebo-controlled trial. The trial consisted of three 12-week periods-a double-blind treatment period, an open-label efalizumab treatment period, and a safety follow-up. Results: There were no statistical differences between treatment groups in percent hair regrowth, quality-of-life measures, or changes in biologic markers of disease severity after 12 or 24 weeks. In both groups, there was an approximately 8% response rate for hair regrowth (at 12 weeks). Efalizumab was well tolerated. Limitations: Numbers were too small for certain analyses. Conclusion: A 3- to 6-month trial of efalizumab was not effective in promoting hair regrowth in this small cohort of patients with moderate-to-severe AA.