Background: Bladder cancer is a major health problem, especially among men. Opium addiction can be an important risk factor. One important question is whether it can affect the age of onset of bladder cancer. We performed this study to evaluate this question. Materials and Methods: In a cross-section study, records of patients diagnosed with bladder carcinoma in Shahid Labbafinejad Medical Center, within 1999-2008 were included. Data were extracted from records regarding age at onset, gender, smoking status, and opioid addiction and analyzed with SPSS 13. Results: Within 10 years, 920 cases were diagnosed with bladder cancer of which 97 percent were transitional cell carcinoma. In 698 cases, opium addiction status was recorded in 21.3% (n=149). Age at diagnosis was $59.7{pm}11.51$ (median: 60) among opioid addicts which was significantly lower than nonaddicts ($63.1{pm}13.65$, Median: 65) (P<0.001). Conclusions: Opium addiction can decrease the age of onset of bladder cancer.