Certolizumab pegol (CZP) is an Fc-free, PEGylated anti-tumour necrosis factor biologic. To report the 3-year efficacy of CZP in plaque psoriasis, pooled from the CIMPASI-1 (NCT02326298) and CIMPASI-2 (NCT02326272) phase III trials. Adults with moderate-to-severe psoriasis for ≥ 6 months were randomized 2 : 2 : 1 to CZP 200 mg, CZP 400 mg or placebo, every 2 weeks (Q2W) for up to 48 weeks. Patients entering the open-label period (weeks 48-144) from double-blinded CZP initially received CZP 200 mg Q2W. Patients not achieving ≥ 50% improvement in Psoriasis Area and Severity Index (PASI 50) at week 16 entered an open-label CZP 400 mg Q2W escape arm (weeks 16-144). Dose adjustments based on PASI response were permitted during open-label treatment. Outcomes included PASI 75, PASI 90 and Physician's Global Assessment (PGA) 0/1 responder rates, based on a logistic regression model (missing data imputed using Markov Chain Monte Carlo methodology). In total, 186 patients were randomized to CZP 200 mg Q2W and 175 to CZP 400 mg Q2W. At week 48, PASI 75/90 was achieved by 72·7%/51·3% of patients randomized to CZP 200 mg and 84·4%/62·7% randomized to CZP 400 mg. Patients entering the open-label period at week 48, from blinded treatment, received CZP 200 mg Q2W. At week 144, PASI 75/90 was achieved by 70·6%/48·7% patients randomized to CZP 200 mg and 72·9%/42·7% randomized to CZP 400 mg. At week 16, 72 placebo-randomized patients entered the CZP 400 mg Q2W escape arm; 75.7%/58.5% achieved PASI 75/90 at week 144. Both CZP 200 mg and 400 mg Q2W demonstrated sustained, durable efficacy, with numerically higher responses for some outcomes with 400 mg Q2W. © 2020 The Authors. British Journal of Dermatology published by John Wiley & Sons Ltd on behalf of British Association of Dermatologists.