Although histologic heterogeneity of lung cancer is well recognized, little information is available related to possible effects of this heterogeneity on prognosis. We collected 100 consecutive lung cancer cases, including 35 autopsies and 65 surgical resections, which were extensively sampled (average, ten blocks per case) and analyzed for histologic heterogeneity. Slides were randomized and classified by five pathologists using the 1981 World Health Organization (WHO) classification scheme. Five-year follow-up data were obtained for the surgical cases, and detailed information on staging and survival from time of diagnosis was available in 91 cases. Survival time was analyzed with respect to the patient's age, sex, stage, predominant histologic pattern, and presence or absence of major heterogeneity. The latter is defined as the presence on at least one slide of a major histologic pattern different from that of the remaining slides for that case. The only statistically significant predictor of survival was tumor stage (P less than 0.0001). Heterogeneous tumors appeared to have a worse survival, but this did not reach statistical significance. There was no relationship between survival and predominant histologic pattern (cell type), sex, or age.