The patterns of risk by histologic type of lung cancer were analyzed with the use of data from a large hospital-based case-control study (7,804 cases and 15,207 controls) of lung cancer performed in Western Europe. Relative risks (RR) increased with duration of cigarette use for all histologic types, although the gradients of risk were greater for Kreyberg I cell types, particularly squamous cell carcinoma (SCC), than for adenocarcinoma (AC). Risks also declined more sharply with years since cessation of smoking for all Kreyberg I cell types, in particular for SCC, rather than for AC. After adjustment for duration of use, the RR associated with number of cigarettes smoked per day, frequency and depth of inhalation, and fraction of cigarette consumed were not consistently different by cell type, suggesting that intensity-related measures of cigarette exposure have less effect on cell type than duration-related factors. Among those who never smoked there were marked cell type differences by sex, with a greater proportion of AC compared to SCC for females (45 vs. 25%) than for males (35 vs. 33%). Review of limited work histories indicated that occupational associations also were more strongly related to Kreyberg I than to Kreyberg II tumors.