A retrospective cohort study of workers exposed to phenoxy herbicides, chlorophenols, and contaminants (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other polychlorinated dioxins and furans) has been conducted in a chemical factory in the Netherlands. Male workers exposed to phenoxy herbicides or chlorophenols showed increased relative risks (adjusted for age, calendar period at end of follow-up, and time since first exposure/employment) for total mortality (relative risk (RR) = 1.8, 95% confidence interval (Cl) 1.2–2.5), cancer mortality (RR = 4.1, 95– Cl 1.8–9.0), respiratory cancer (RR 7.5, 95% Cl 1.0–56.1), non-Hodgkin's lymphoma (RR = 1.7, 95% Cl 0.2–16.5), and =ischemic heart diseases (RR = 1.8, 95% Cl 0.9–3.6) compared with an internal referent group of nonexposed workers. By using TCDD levels (predicted at the time of maximum exposure), based on extrapolated TCDD levels that were measured in a subset of the cohort, estimated relative risks for workers with medium and high TCDD levels were comparable with risks derived from the simple and earlier applied dichotomous exposure classification. In general, relative risks were highest in the highest category, indicating exposure-related increases in risk with TCDD level. In conclusion, results of this cohort study support the evidence of a high cancer risk in workers exposed to phenoxy herbicides, chlorophenols, and contaminants. Am J Epidemiol 1998; 147:891–901.