Objectives Uveitis, psoriasis and inflammatory bowel disease (IBD) are common extra-articular manifestations (EAM) in patients with ankylosing spondylitis (AS); however, summary data of reported prevalence are lacking. The aim of the present study was to summarise the prevalence of EAMs among patients with AS and to identify underlying factors to explain potential heterogeneity of prevalence. Methods A systematic literature search was performed (Medline, Embase and Cochrane Library) to identify relevant articles. Risk of bias was assessed and data were extracted. Pooled prevalences were calculated. Potential sources of any observed clinical or methodological heterogeneity in the estimates were explored by subgroup and metaregression analysis. Results In the 156 selected articles, 143 reported the prevalence of uveitis (44 372 patients), 56 of psoriasis (27 626 patients) and 69 of IBD (30 410 patients). Substantial heterogeneity was observed in prevalence estimates among all EAMs (I2= 84-95%). The pooled prevalence of uveitis was 25.8% (95% CI 24.1% to 27.6%), and was positively associated in multivariable metaregression with disease duration (beta 0.05, 95% CI 0.03 to 0.08) and random selection of patients (beta -0.24, 95% CI -0.43 to -0.04). The pooled prevalence of psoriasis was 9.3% (95% CI 8.1% to 10.6%). The pooled prevalence of IBD was 6.8% (95% CI 6.1% to 7.7%) and was positively associated with the percentage of women in the studies (beta 0.02, 95% CI 0.00 to 0.03). Geographical area was associated in multivariable metaregressions with prevalence of all EAMs. Conclusions EAMs are common in patients with AS. The large heterogeneity between studies can be partly explained by differences in clinical as well as methodological characteristics.