OBJECTIVES: The U.S. Food and Drug Administration issued a statement indicating that pioglitazone, one of the type II diabetes oral hypoglycemic agents, may potentially increase the risk of developing bladder cancer in 2010. This study examined the relationship between pioglitazone and incidence rate of bladder cancer among type 2 diabetes patients in Taiwan by population-based data without financial support from any institution.  METHODS: We analyzed 8 years cohort (2003-2010) in Taiwan by using National Health Insurance Database. Approximately 2 million randomly sampled representative beneficiaries from the National Health Insurance database were used as the data source for analysis. Totally 4,765 patients used pioglitazone were followed and compared with 4,765 control cases selected by propensity score matched approach.  RESULTS: We found that risk of bladder cancer increases with age, and risk increased higher for men than women, with a hazard ratio of 1.8. With propensity score matching, no significant correlation was found between the risk of bladder cancer and pioglitazone using. There was no significant difference in survival curves between patients ever used and never used pioglitazone. There is a tendency of getting bladder cancer earlier for patients ever used compared to never users yet it is not statistically significant.  CONCLUSIONS: A significant increase risk of bladder cancer is observed for patients ever used compared to all diabetes patients who never used pioglitazone; however, the risk diminishes after adjusting with propensity score matching. Our study results indicated that the potential hazard of pioglitazone might be overestimated.