Objectives : Using the population-based cancer registry in Jejudo, we found that Jejudo had lower incidence in stomach cancer than other regions in Korea. The aim of this study was to evaluate reasons for this difference. Methods : Citrus is the leading agricultural production in Jejudo, suggesting that lower cancer incidence in Jejudo could be explained by citrus fruit intake. We evaluated this hypothesis with quantitative systematic review(QSR). Results : Stomach cancer incidence was significantly lower, with a summary odds ratio(SOR) after QSR of 0.72 [95% CI=0.64-0.81]. In addition, the SOR of pancreatic cancer tended to be lower at 0.83 [95% CI=0.70-0.98]. The SOR of prostate cancer was slightly higher at 1.03 [0.89-1.19]. Conclusions : Quantitative systematic reviews for the effect of citrus fruit intake on cancer occurrence suggested that lower cancer incidence in Jejudo could be explained by intake of citrus fruits.