Introduction <p>Adherence to biologics is crucial for the effective management of patients with inflammatory bowel disease (IBD). However, comprehensive data on the prevalence of adherence is still lacking.</p> Aim <p>This systematic review and meta-analysis aimed to estimate the prevalence of adherence to biologics among adult patients with IBD and to identify the factors influencing adherence.</p> Method <p>We conducted a systematic search of PubMed, Embase, Scopus, CINAHL, Web of Science, the Cochrane Library, and three Chinese databases for relevant observational studies published between January 1, 2010, and March 15, 2025. A random-effects model was employed to calculate the pooled prevalence of adherence. Heterogeneity and publication bias were assessed. We classified the identified influencing factors and conducted a narrative synthesis to summarize the findings.</p> Results <p>This review included 29 studies involving 44,397 patients with IBD from 14 countries. The pooled prevalence of adherence to biologics was 70% (95% CI 66%–75%, I² = 98.9%). Subgroup analyses indicated that higher adherence was likely among patients from upper-middle-income countries, those assessed with validated subjective tools, patients with CD, and those receiving subcutaneous biologics. Studies with cross-sectional designs and lower methodological quality also tended to report higher adherence. Gender and insurance status were identified as key factors influencing adherence, consistently supported by at least three studies.</p> Conclusion <p>The results suggested that adult patients with IBD exhibit moderately high levels of adherence to biologics. Gender and insurance status were factors associated with adherence. Given that these conclusions are limited by heterogeneity and methodological diversity, further validation through high-quality studies is required.</p>