In a population-based case-control study in Germany, 540 incident cases of colorectal cancer (CRC) aged > or =30 years and 614 controls were recruited from January 2003 to June 2004. Information on risk factors of CRC and lifetime history of active smoking and exposure to environmental tobacco smoke (ETS) was obtained by personal interviews. This analysis is limited to never smokers (252 cases and 292 controls). Associations were assessed using conditional logistic regression models adjusting for potential confounders. We found no evidence of an increased risk of CRC following exposure to ETS overall, in childhood or at work. For spousal exposure, we, however, found a significant risk increase for women currently exposed (OR: 3.54; 95% CI: 1.03-12.15) and for women exposed to >23 pack-years of spousal smoking (OR: 3.02; 95% CI: 0.99-9.28). Our findings do not indicate a major impact of ETS on CRC risk but suggest that risk may be increased following spousal exposure.