Psychological stress is recognized as a factor that contributes to increased susceptibility to a number of diseases, including cancer. Psychological stress, via release of chemical mediators, can induce long-term changes in the organism resulting in an altered responsiveness of the organism to external carcinogens. The present investigation sought to evaluate the impact of stress on polycyclic aromatic hydrocarbon (PAH)-induced carcinogenesis. We utilized a repetitive restraint stress mouse model and the model PAH, 7,12-dimethylbenz[a]anthracene (DMBA). Restraint stress was applied three times a week for 6 weeks and DMBA was administered intra-gastrically once a week for 6 weeks and formation of skin, mammary and ovarian tumours was examined at 26 weeks by pathological analyses. The results indicate that stress accelerates the onset of tumour formation produced in response to DMBA and significantly influences the type and location of tumours. Taken together, these results demonstrate that stress enhances the carcinogenicity of DMBA. These results clearly indicate the need for further characterization of the impact of stress on carcinogen metabolism in oncology.