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BACKGROUND AND AIMS To summarize the epidemiological evidence and assess the validity of claimed associations of inflammatory bowel diseases (IBD) with overall and site-specific cancer risk. METHODS We systematically searched PubMed, Embase and Scopus from inception to May 10, 2021 to identify and comprehensively re-analyze the data of meta-analyses on associations between IBD (i.e. Crohn's disease [CD] and ulcerative colitis [UC]) and subsequent risk of cancer. The strength of epidemiological evidence was graded into high, moderate or weak, applying prespecified criteria, which included the random effects estimate, its 95% confidence interval and p-value, estimates of heterogeneity, small-study effects, and robustness to unmeasured confounding. RESULTS This study critically appraised 277 estimates derived from 24 published meta-analyses and authors' own meta-analyses. The association between pediatric-onset IBD and overall risk of cancer showed high epidemiological evidence. Twenty associations (15 cancer types) demonstrated moderate evidence: any cancer (pediatric-onset UC), mouth to terminal ileum (CD), small bowel (CD/UC), colon (CD), rectum (CD/UC), colon-rectum (IBD, pediatric-onset CD/UC), bile ducts and liver (CD/UC), liver (CD), intrahepatic cholangiocarcinoma (IBD), bile ducts (CD), skin (CD), squamous cell carcinoma of the skin (CD), non-melanoma skin cancer (UC), kidney (CD) and thyroid cancer (IBD). Another 40 associations (23 cancer types) showed statistical significance; however, our confidence in these effect estimates was weak. No statistical significance was found regarding further 47 associations. CONCLUSION Associations between IBD and different types of malignancy showed varying levels of evidence and magnitude of risk. Further primary research investigating the impact of a consistent set of risk factors that are known to affect cancer risk is warranted.