At 12 weeks, the percentage of patients with a reduction in the PASI score by at least 75% was significantly greater with ixekizumab (except with the lowest, 10-mg dose) ― 150 mg (82.1%), 75 mg (82.8%), and 25 mg (76.7%) ― than with placebo (7.7%, P<0.001 for each comparison), as was the percentage of patients with a reduction in the PASI score by at least 90%: 150 mg (71.4%), 75 mg (58.6%), and 25 mg (50.0%) versus placebo (0%, P<0.001 for each comparison). Similarly, a 100% reduction in the PASI score was achieved in significantly more patients in the 150-mg group (39.3%) and the 75-mg group (37.9%) than in the placebo group (0%) (P<0.001 for both comparisons). Significant differences occurred at as early as 1 week and were sustained through 20 weeks. Adverse events occurred in 63% of patients in both the combined ixekizumab groups and in the placebo group. No serious adverse events or major car diovascular events were observed. Conclusions Use of a humanized anti–interleukin-17 monoclonal antibody, ixekizumab, improved the clinical symptoms of psoriasis. Further studies are needed to establish its long-term safety and efficacy in patients with psoriasis. (Funded by Eli Lilly; ClinicalTrials.gov number, NCT01107457.)