To identify subgroups of oral cavity and pharynx (OCP) cancers that may be etiologically distinct, we evaluated age-adjusted incidence rates by histologic type, anatomical site, race, and sex using cases diagnosed during 1975-1998 in nine US Surveillance, Epidemiology, and End Results (SEER) program registries. Male/female rate ratios were about one for adenocarcinoma (AC), three or more for squamous cell carcinoma (SCC), and undetermined for Kaposi's sarcoma (KS). Among males, black/white rate ratios exceeded two for cancers of the palate, tonsil, oropharynx, and pyriform sinus, and were less than one only for lip and salivary gland cancers. Among females, rates by race were similar for all oral sites except lip, but rates for each of the pharynx subsites were higher among blacks. Findings suggest that OCP cancers may be separated into SCC of the lip, SCC of the oral cavity, SCC of the pharynx, AC, and KS.