Standard methods for analysis of case–control studies were used. The mean delay from diagnosis to interview was subtracted from the date of interview to calculate a reference date for duration of exposure for each control. Tertiles of cannabis use were determined by the marginal distribution ofuse for all subjects to reduce the chance of zero cell counts if just the control group was used. Relative risks (RRs) were estimated by calculating odds ratios by logistic regression and adjusted for confounding variables. Adjustment for age, joint- yrs of cannabis smoking and pack-yrs of cigarette smoking was made by including them as continuous variables in the regression models. The effects of categories of pack-yrs of cigarette smoking (quintiles of smoking for all subjects interviewed) and joint-yrs of cannabis smoking (tertiles of use for all subjects interviewed) were also assessed.