This analysis describes the epidemiology of in situ head and neck carcinomas (anatomic sites of lip, oral cavity, pharynx, larynx) about which there is limited knowledge. Data were derived from nine population-based cancer registries participating in the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program. SEER annual age-adjusted incidence rates for in situ head and neck carcinomas increased from 6.33/1,000,000 person-years (PY) in 1976 to 8.04/1,000,000 PY in 1995 [percent change (PC)=35%, P<0. 001]. From 1976 to 1995 age-adjusted changes in incidence by anatomic site ranged from 53% PC (larynx) to -11% PC (lip) (both P<0. 005). Incidence and survival associated with in situ head and neck carcinomas varied by anatomic site, age, sex, and race and did so in a pattern similar to that seen for invasive carcinomas of this region. However, the climbing incidence of in situ carcinoma, which may be related to increased surveillance, contrasts sharply with the declining incidence of invasive carcinoma.