© 2017 British Association of Dermatologists Background: Little is known about the role of the HLA-C*06 allele in the response to psoriasis treatments. Objectives: To confirm the role of HLA-C*06 as a pharmacogenetic marker of response to ustekinumab in a new, large cohort of patients involving four European centres. Methods: In this retrospective multicentre study we reviewed data of 255 patients with psoriasis genotyped for HLA-C*06 who started ustekinumab treatment between January 2014 and March 2015. The severity of psoriasis and response to treatment were evaluated using the Psoriasis Area and Severity Index (PASI) score at baseline and then at follow-up visits on weeks 4, 12, 28, 40 and 52. The primary end point was the proportion of patients achieving ≥ 50% reduction in PASI score (PASI 50) at week 4. A ≥ 75% reduction in PASI score (PASI 75) and a ≥ 90% reduction in the PASI score (PASI 90) after 12 weeks were secondary end points. Results: At week 4, PASI 50 was seen in 71·7% of HLA-C*06-positive (C*06POS) and 35·2% of HLA-C*06-negative (C*06NEG) patients. At week 12, PASI 75 was reached by 69.1% of C*06POS patients and 40·5% of C*06NEG patients. After 52 weeks, PASI 75 was reached by 83.7% of C*06POS patients and 58.8% of C*06NEG patients. Conclusions: The results from our new, large cohort of European patients treated with ustekinumab in daily clinical practice confirm the role of HLA-C*06 as a potential predictor of response to ustekinumab.