Background <p>Non-alcoholic fatty liver disease (NAFLD) has been frequently reported as a relatively common comorbidity in patients with inflammatory bowel disease (IBD). We aimed to calculate the prevalence of NAFLD and related terms like MAFLD (metabolic dysfunction-associated fatty liver disease) and MASLD (metabolic dysfunction-associated steatotic liver disease) in IBD (inflammatory bowel disease) patients by reviewing and analyzing the most recent evidence.</p> Main body <p>We systematically searched PubMed, Web of Science, Scopus, EMBASE, and ProQuest databases for studies published between January 01, 2001 and December 31, 2024. Eligible studies included cohort and cross-sectional designs that reported the prevalence of NAFLD in IBD patients. Studies were screened according to inclusion and exclusion criteria and subsequently evaluated. A total of 34 studies were included in our systematic review, of which 32 studies were eligible for meta-analysis. The overall pooled prevalence of NAFLD in IBD patients was 32.3% CI95% (27.3 to 37.3%), (<i>I</i>² = 98.97%), with a prevalence of 31.3% CI95% (22.7 to 39.8%) (<i>I</i>² = 98.78%) in Crohn’s disease (CD) and 27.1% CI95% (20.3 to 33.9%) (<i>I</i>² = 96.69%) in ulcerative colitis (UC). NAFLD was found to be more common in male IBD compared to females. Diagnostic modality influenced prevalence rates, with controlled attenuation parameter (CAP) reporting a higher prevalence (36.6% CI95% (32.4 to 40.9%) (<i>I</i>² = 70.54%)) compared to other methods. Liver fibrosis was also examined as an important comorbidity and complication among IBD patients. Based on the included studies, the overall prevalence of fibrosis in IBD was 7.3% (5.5 to 9.1%) (<i>I</i>² = 80.99%).</p> Conclusion <p>About one-third of IBD patients are likely to present with NAFLD. Evolving definitions of NAFLD such as MAFLD highlight the urgent need for international standardization and much more studies in this area.</p> Trial registration <p>PROSPERO CRD420250651182</p>