OBJECTIVES: Marijuana smoking has been implicated as a causative factor in traditionally tobacco-related tumors of the head and neck and of the lung. When associated with marijuana use, such tumors occur in a much younger patient population than do similar tumors in tobacco smokers. Owing to the large number of young men with a history of marijuana presenting with transitional cell carcinoma to VA facilities, this study was designed to compare the marijuana use among young (aged less than 60 years) transitional cell carcinoma patients with that among age-matched controls. METHODS: Fifty-two men aged less than 60 years presenting consecutively with transitional cell carcinoma and 104 age-matched controls (defined by having no history of transitional cell carcinoma, hematuria, or irritative voiding symptoms, as well as unremarkable results on urinalysis and urine cytology) completed questionnaires about exposure to various potential carcinogens, including radiation, Agent Orange, smoked or processed meats, dyes, tobacco, and marijuana. RESULTS: Of the 52 transitional cell carcinoma patients, 46 (88.5%) reported a history of habitual marijuana usage, and 72 (69.2%) of the age-matched controls gave a history of habitual marijuana use. This difference was statistically significant (P = 0.008). In those with transitional cell carcinoma, marijuana use significantly correlated with tumor stage, grade, and number of recurrences. CONCLUSIONS: Marijuana smoking might increase the risk of transitional cell carcinoma.