In reported systematic reviews and meta-analyses of randomized controlled trials (RCTs) assessing treatments for psoriasis, the proportion of serious adverse events (SAEs) did not differ between treatments and placebo. Including cases of psoriasis worsening as SAEs may explain the lack of difference. This systematic review and meta-analysis aimed to explore this possibility. Among the 140 RCTs included in the Living Network Cochrane Review (last search on 8 May 2019), we selected those comparing a biologic treatment against placebo. The primary outcome was the numbers of SAEs in the treatment and placebo arms after excluding cases of psoriasis worsening. Secondary outcomes were the number of adverse events (AEs) of special interest. The trial was registered on PROSPERO (CRD42019124495). We analysed 51 RCTs. Of these, 21 included at least one anti-tumour necrosis factor (TNF)-α arm, 15 one anti-interleukin (IL)-17 arm, 11 one anti-IL-23 arm and nine one anti-IL-12/23 arm. With cases of psoriasis worsening included, the risk of occurrence of SAEs between biologic treatments and placebo did not differ: risk ratio (RR) 1·09, 95% confidence interval (CI) 0·88-1·36. After excluding cases of psoriasis worsening, the RR became significant (RR 1·30, 95% CI 1·02-1·65). By drug class, the RRs were for anti-TNF-α, 1·68 (95% CI 1·11-2·54; no missing data); anti-IL-17, 1·28 (95% CI 0·88-1·85; no missing data); anti-IL-23, 0·95 (95% CI 0·59-1·52; no missing data) and anti-IL-12/23, 1·18 (95% CI 0·72-1·94; no missing data). We were unable to examine potential differences in AEs of special interest between biologic treatments and placebo arms because of the small number of events. On excluding cases of worsening psoriasis, the risk of occurrence of SAEs is higher in the biologic than in the placebo arm. Given the rare events, we could not highlight whether this higher risk of SAEs was related to AEs of special interest. Reporting of SAEs in clinical trials has to be changed to provide more transparency through the separate reporting of disease flares leading to hospital admission and other SAEs. © 2020 British Association of Dermatologists.