Pioglitazone, an antidiabetic drug, became available in the UK in 2000 and is mainly used in combination with a diet and exercise programme and other anti-diabetic medications to treat type 2 diabetes mellitus. A recent observational study  using the Kaiser Permanente Northern California diabetes registry data found that among 193 099 diabetic patients who were ≥40 years old, use of pioglitazone at any time (n= 30 173) was not associated with risk of bladder cancer (adjusted hazard ratio (HR) 1.2 [95% CI 0.9, 1.5]). However, long term use of pioglitazone (>24 months of therapy) was associated with an increased risk of bladder cancer (adjusted HR 1.4 [95% CI 1.03, 2.0]). More recent data from observational studies report relative risks ranging from 1.12 to 1.33 when diabetic patients receiving pioglitazone are compared with diabetic patients receiving other antidiabetic medicines but not exposed to pioglitazone . We have performed a propensity score matched cohort study, the methodology of which minimizes the chance of finding a spurious result . The study was performed in the General Practice Research Database (GPRD), a large, well-validated UK based primary care database established in the late 1980s  to examine whether pioglitazone use was associated with increased risk of bladder cancer compared with other oral anti-diabetic treatments.