Exposure to environmental tobacco smoke (ETS) poses serious health risks for children with cancer. Parental smoke is a primary source of exposure for these children. Parent smoking behaviors and parent-reported ETS exposure among children treated for cancer were examined in this study. In addition, reports of ETS exposure among children with cancer who currently smoked or who had smoked in the past were compared to those of children with cancer who never smoked. Written questionnaires about smoking behaviors and ETS exposure were administered to 47 smoking parents of youngsters diagnosed with cancer, 10-18 years of age (57.4% male, 78.7% Caucasian). Child reports of smoking status were also obtained. Results indicated that children with cancer are exposed to ETS from a number of sources and settings, as reported by their parents. Current or previous child smokers had greater ETS exposure than non-smoking children. Older children and Caucasian children also had greater ETS exposure. Level of ETS exposure did not differ based on the child's treatment status. Interventions that teach parents to protect their youngster from ETS exposure have potential for reducing adverse health outcomes in this vulnerable population.