Background: Safety is an important consideration in decisions on treatment for patients with moderate-to-severe psoriasis and the study of drug safety is the main purpose of the BIOBADADERM registry. The combination of a biologic agent and a conventional systemic drug [generally methotrexate (MTX)] is a common treatment in clinical practice. However, there is a paucity of evidence from real-world practice on the safety of such combination regimens in the treatment of psoriasis., Objectives: The primary objective of this study was to ascertain whether the use of regimens combining biologic drugs with MTX in the management of moderate-to-severe psoriasis increases the risk of adverse events (AEs) or serious AEs (SAEs). We compared monotherapy using tumour necrosis factor (TNF), interleukin (IL)-17 and IL-23 inhibitors with the use of the same drugs in combination with MTX., Methods: Using data from the BIOBADADERM registry, we compared biologic monotherapies with therapies that were combined with MTX. We estimated adjusted incidence rate ratios (aIRR) using a random effects Poisson regression with 95% confidence intervals for all AEs, SAEs, infections and serious infections and other AEs by system organ class., Results: We analysed data from 2829 patients and 5441 treatment cycles, a total of 12 853 patient-years. The combination of a biologic with MTX was not associated with statistically significant increases in overall risk of AEs or SAEs in any treatment group. No increase in the total number of infections or serious infections in patients receiving combined therapy was observed for any group. However, treatment with a TNF inhibitor combined with MTX was associated with an increase in the incidence of gastrointestinal AEs (aIRR 2.50, 95% CI 1.57-3.98; P < 0.002)., Conclusions: The risk of AEs and SAEs was not significantly increased in patients with moderate-to-severe psoriasis receiving different classes of biologic drugs combined with MTX compared with those on biologic monotherapy., Competing Interests: Conflicts of interest J.M.C. has participated as a speaker and/or advisor and/or principal investigator/senior investigator in clinical trials sponsored by for Celgene, Janssen, Lilly, Leo Pharma, Novartis, Pfizer, MSD, Biogen, Mylan, Amgen, AbbVie and Sandoz. A.G.-Q. acted as consultant and/or speaker for and/or participated in clinical trials as principal investigator and subinvestiator for AbbVie, Almirall, Amgen, Boehringer, Janssen, Leo Pharma, Lilly, Novartis, MSD, Pfizer-Wyeth and UCB. R.R.-D. acted as consultant and/or speaker for and/or participated in clinical trials as principal investigator for AbbVie, Almirall, Amgen, Boehringer, Janssen, Leo Pharma, Lilly, Novartis, MSD, Pfizer-Wyeth and UCB. A.S.-T. has served as a consultant and/or paid speaker for and/or participated in clinical trials sponsored by companies that manufacture drugs used for the treatment of psoriasis, including AbbVie, Celgene, Janssen-Cilag, LEO Pharma, Lilly, Novartis and Pfizer. M.L.-V. acted as a consultant and speaker and participated in clinical trials for Janssen-Cilag, AbbVie, Boehringer, Celgene, Pfizer, Novartis, Lilly, Almirall, UCB, Kyowa Kirin and Leo Pharma. E.H.-A. has served as consultant and/or speaker with Leo Pharma, Novartis, Janssen, Lilly, Celgene and AbbVie. P.d.l.C. acted as a consultant and/or speaker for Janssen-Cilag, AbbVie, MSD, Pfizer, Novartis, Lilly, Almirall, UCB, Biogen, Celgene, Amgen, Sandoz, Sanofi and Leo Pharma. O.B.-R. acted as a consultant and/or speaker for Janssen-Cilag, AbbVie, Pfizer, Novartis, Lilly, Celgene, Leo Pharma, Amgen, Boehringer, UCB and Almirall. L.L.-E. participated as advisory board member and received educational grants from Janssen, AbbVie, MSD, Lilly, Novartis, LeoPharma and Pfizer. I.B. acted as a consultant and/or speaker for and/or participated in clinical trials sponsored by companies that manufacture drugs used for the treatment of psoriasis, including Janssen Pharmaceuticals Inc., Almirall SA, Lilly, AbbVie, Novartis, Celgene, Biogen Amgen, Leo Pharma, UCB, Pfizer-Wyeth and MSD. M.F. has participated as speaker and/or advisor for Janssen, Lilly, Novartis, Pfizer, MSD, AbbVie Celgene and Almirall. A.M. acted as consultant and/or speaker for AbbVie, Almirall, Celgene, Janssen, Leo Pharma, Lilly, Novartis. L.R. acted as a consultant and speaker for Janssen-Cilag, AbbVie, MSD, Pfizer, Novartis, Lilly, Almirall, Celgene and Leo Pharma. J.R.-M. acted as a consultant and/or speaker for and/or participated in clinical trials sponsored by AbbVie, Almirall, Janssen, Leo Pharma, Novartis, UCB, Pfizer, Lilly, Amgen and Boehringer Ingelheim. G.C. has been reimbursed by Janssen, AbbVie, Novartis, Pfizer, MSD and Celgene for advisory service and conference attendance. C.G.-D. participated as advisory board member for AbbVie, Almirall and speaker for Janssen, Lilly and Celgene. C.P.-M. acted as a consultant and/or speaker for Janssen-Cilag, AbbVie, MSD, Pfizer, Novartis, Lilly, Almirall, UCB, Celgene and Leo Pharma. E.D.A. has participated as a speaker and/or and/or PI/SI clinical trials sponsored by Amgen, Almirall, Janssen, Lilly, Leo Pharma, Novartis, UCB and AbbVie. J.A.S.-P. has served as consultant and/or speaker with Leo Pharma, Novartis, Janssen, Lilly, Celgene, AbbVie, Amgen, Sanofi, Almirall and Pfizer. D.P.R.-G. has been reimbursed by Pfizer, Janssen, Celgene, AbbVie, Novartis and LeoPharma for advisory services and conference attendance. I.G.D. received travel grants for congresses from AbbVie, MSD, Pfizer and Sanofi., (© The Author(s) 2023. Published by Oxford University Press on behalf of British Association of Dermatologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)