This work reviews the literature concerned with the carcinogenesis of silicon in humans. Many of the studies deal with large cohorts of industrial workers. We sort these according to the type of silicon exposure and its consequences. An association of silica dust and fibers with lung and stomach cancers is widely reported and still other types of cancer are linked to silicon exposure. The risk is far greater if silicosis is present. On the other hand, still other studies show no association between silicon and cancer in humans, especially when confounding variables such as smoking and concomitant exposure to other carcinogens are taken into consideration. Though the literature is controversial, the weight of evidence nevertheless strongly supports an important role for silicon in the production of cancer in humans.