Suspicions have recently arisen that cancer of the lip may exert an undue influence on overall oral cancer statistics and, therefore, possibly distort the true image of intraoral cancer. The authors investigated this question through epidemiologic analysis. A total of 2291 cases of lip cancer accessioned by the Connecticut Tumor Registry (CTR) from 1935 to 1985 (23.6% of all oral cancer) were analyzed. Occurrence trends for males and females had different patterns: for men, the age-adjusted incidence rates showed a fivefold decrease during the 51- year study; for women, the rates were relatively low and constant during the same period. Analysis for age-specific rates revealed that the older the age group, the higher the incidence rates for both sexes. Squamous cell carcinoma accounted for at least 87.4% of all lip cancers (96.2% if nonspecified epithelial neoplasms are assumed to be squamous cell carcinoma). The vermilion border of lower lip was the most common site. Moderately differentiated tumors were most common (48.5%), closely followed by well-differentiated tumors (44.2%). Analysis by county showed that the crude incidence rates for males in New London and Windham counties exceeded the average Connecticut statewide rates. The authors concluded that the epidemiology of Connecticut lip cancer differs significantly from that of intraoral squamous cell carcinoma in the same population studied within the same period of time. Epidemiologic studies involving "oral cancer" should direct attention to anatomic subsite to consider differences in disease trends according to specific location.