Background The association between fluoropyrimidines except for capecitabine and the risk of hypertriglyceridemia is unclear. Objective To investigate hypertriglyceridemia in patients receiving fluoropyrimidines. Method This observational study used anonymized patient data recorded in the open-access Japanese Adverse Drug Event Report database. All fluoropyrimidine and taxane users were investigated. Results We identified 29,451 fluoropyrimidine users and 21,266 taxane users. Disproportionality for both hypertriglyceridemia and an increase in serum triglyceride levels was observed in fluoropyrimidine users compared with in taxane users (reporting odds ratio, 6.74; 95% confidence interval [CI] 2.05-22.17; P < .001). Multivariate logistic analysis showed that both hypertriglyceridemia and an increase in serum triglyceride levels among fluoropyrimidines users were significantly associated with doxifluridine use (odds ratio [OR] 42.50; 95% CI 5.34-338.00; P < .001), tegafur use (OR 9.56; 95% CI 2.08-43.90; P < .001), capecitabine use (OR 12.30; 95% CI 2.67-56.80; P < .001), and breast cancer (OR 5.61; 95% CI 1.07-29.50; P = .042). Conclusion This study suggests that the use of tegafur and doxifluridine is associated with an increased risk of hypertriglyceridemia similar to that with the use of capecitabine; in particular, fluoropyrimidine users with breast cancer may have a high risk of hypertriglyceridemia.