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Aims Differentiating pterygium from ocular surface squamous neoplasia (OSSN) is important for guiding management. This meta-analysis evaluates the prevalence and risk factors for incidental OSSN in clinically diagnosed pterygia.Methods Ovid Embase, MEDLINE, Cochrane Library and Web of Science were systematically searched from January 2000 to February 2025. Included studies analysed ≥100 clinically diagnosed pterygia via histopathology. Random-effects meta-analysis assessed the prevalence of incidental OSSN among pterygia. Risk factors were evaluated using the Mantel-Haenszel and inverse variance methods, and meta-regression analysed the influence of publication year, geographic proximity to the equator, and country-level ultraviolet (UV) radiation exposure.Results 12 studies, comprising 8688 specimens, identified 202 cases of incidental OSSN (pooled prevalence=1.32%, 95% CI 0.41% to 4.21%, I 2=95.3%). Meta-regression revealed that lower OSSN prevalence was associated with greater distance from the equator (OR 0.49, 95% CI 0.28 to 0.83, p<0.01), while higher prevalence was associated with greater UV exposure (OR 2.20, 95% CI 1.17 to 4.14, p=0.01). Publication year had no effect (p=0.98). Age (p=0.18), sex (p=0.45) and lesion location (p=0.60–0.82) did not differ between incidental OSSN cases and benign pterygia. Incidental OSSN prevalence also did not differ between primary and recurrent pterygia (p=0.23). Regional analyses revealed variation in prevalence: Europe (0.29%), Asia (0.76%), North America (1.03%), Oceania (8.57%) and South America (14.97%).Conclusions This meta-analysis, based on low- to very low-certainty evidence, identified a 1.32% pooled prevalence of incidental OSSN in clinically diagnosed pterygia, highlighting the potential influence of UV exposure and equatorial proximity. The overlap in demographic and lesion characteristics between benign pterygia and OSSN underscores diagnostic challenges.