There is considerable theoretical evidence that marijuana should be carcinogenic. However, most reviews have found no direct evidence of chronic marijuana smoking causing lung cancer. Some recent reports implicate marijuana smoking as a cause of cancer of the upper aerodigestive tract, though most of the subjects were exposed to other, possibly confounding, etiologic factors, namely tobacco and alcohol. We report two cases of squamous cell carcinoma of the tongue in men who chronically smoked marijuana but had no other risk factors. The totality of cases may point to a predilection of marijuana smoke for carcinogenesis in the upper aerodigestive tract. This correlates with nonmalignant effects and may be related to a different method of smoking marijuana compared with tobacco.