The National Institute for Health and Care Excellence invited Eli Lilly and Company Ltd, the company manufacturing ixekizumab (tradename Taltz®), to submit evidence for the clinical and cost effectiveness of ixekizumab. Ixekizumab was compared with tumour necrosis factor-α inhibitors (etanercept, infliximab, adalimumab), ustekinumab, secukinumab, best supportive care and, if non-biological treatment or phototherapy is suitable, also compared with systemic non-biological therapies and phototherapy with ultraviolet B radiation for adults with moderate-to-severe plaque psoriasis. Kleijnen Systematic Reviews Ltd, in collaboration with Maastricht University Medical Center, was commissioned as the independent Evidence Review Group. This article presents a summary of the company submission, the Evidence Review Group report and the development of the National Institute for Health and Care Excellence guidance for the use of this drug in England and Wales by the Appraisal Committee. The Evidence Review Group produced a critical review of the clinical and cost effectiveness of ixekizumab based on the company submission. The company submission presented three randomised controlled trials identified in a systematic review. All randomised controlled trials were phase III, multicentre placebo-controlled trials including 3866 participants with moderate-to-severe psoriasis. Two trials also included an active comparator (etanercept). All randomised controlled trials showed statistically significant increases in two primary outcomes, static Physician Global Assessment (0,1) and improvement of 75% from baseline in the Psoriasis Area and Severity Index. Ixekizumab was generally well tolerated in the randomised controlled trials, with similar discontinuation rates because of adverse events as placebo or etanercept. The most frequent adverse events of special interest were infections and injection-site reactions. The company submission also included a network meta-analysis of relevant comparators. The Evidence Review Group highlighted some issues regarding the systematic review process and an issue with the generalisability of the findings in that the trials failed to include patients with moderate psoriasis according to a widely used definition. This issue was considered by the Appraisal Committee and the population was deemed generalisable to patients in England and Wales. Based on the network meta-analysis, the Appraisal Committee concluded that ixekizumab was more clinically effective than adalimumab and ustekinumab, and agreed it was likely that ixekizumab was similarly effective compared with secukinumab and infliximab while tolerability was similar to other biological treatments approved for treating psoriasis. The Evidence Review Group's critical assessment of the company's economic evaluation highlighted a number of concerns, including (1) the use of relative outcomes such as Psoriasis Area and Severity Index response to model the cost effectiveness; (2) the exclusion of the consequences of adverse events; (3) the assumption of no utility gain in the induction phase; (4) equal annual discontinuation rates for all treatments; (5) the selection of treatment sequences for consideration in the analyses and; (6) the transparency of the Visual Basic for Applications code used to develop the model. Although some of these issues were adjusted in the Evidence Review Group base case, the Evidence Review Group could not estimate the impact of all of these issues, and thus acknowledges that there are still uncertainties concerning the cost-effectiveness evidence. In the Evidence Review Group base-case incremental analysis, the treatment sequence incorporating ixekizumab in the second line has an incremental cost-effectiveness ratio of £25,532 per quality-adjusted life-year gained vs. the etanercept sequence. Ixekizumab in the first-line sequence has an incremental cost-effectiveness ratio of £39,129 per quality-adjusted life-year gained compared with the treatment sequence incorporating ixekizumab in the second line. Consistent with its conclusion regarding clinical effectiveness, the Appraisal Committee concluded that the cost effectiveness of ixekizumab for treating moderate-to-severe plaque psoriasis was similar to that of other biological treatments, already recommended in previous National Institute for Health and Care Excellence guidance. The committee concluded that the incremental cost-effectiveness ratio was within the range that could be considered a cost-effective use of National Health Service resources.