The follow-up of 727 patients with squamous-cell carcinoma (SCC) of the lip and oral cavity has been used for the risk analysis of multiple primary tumors (MPTs) following SCC of the lip and oral cavity. Age-, gender- and site-specific cancer-incidence rates from the general population have been applied to the appropriate persons-years of follow-up of patients with SCC of the lip and oral cavity. The study indicates that patients with a primary SCC of the lip and oral cavity have, compared with the general population, a significantly elevated risk of developing an additional cancer of the oral cavity and/or pharynx, the risk being 74.7-fold for males and 190.4-fold for females. Furthermore, a 24.6 and 45.3 times higher risk of an additional esophageal tumor was found in males and females respectively. The risk of cancer of the lung and pharynx was less elevated compared with the risk of cancer of the upper digestive tract. No elevated risks were established in organs outside the respiratory and upper digestive tract.