Epidemiological studies of companion animals offer an important opportunity to identify risk factors for cancers in animals and humans. Canine malignant lymphoma (CML) has been established as a model for non-Hodgkin’s lymphoma (NHL). Previous studies have suggested that exposure to environmental chemicals may relate to development of CML. The authors assessed the relation of exposure to flea and tick control products and lawn-care products and risk of CML in a case-control study of dogs presented to a tertiary-care veterinary hospital (2000-2006). Cases were 263 dogs with biopsyconfirmed CML. Controls included 240 dogs with benign tumours and 230 dogs undergoing surgeries unrelated to cancer. Dog owners completed a 10-page questionnaire measuring demographic, environmental, and medical factors. After adjustment for age, weight, and other factors, use of specific lawn care products was associated with greater risk of CML. Specifically, the use of professionally applied pesticides was associated with a significant 70% higher risk of CML (odds ratio-(OR))1.7; 95% confidence interval (CI))1.1-2.7). Risk was also higher in those reporting use of self-applied insect growth regulators (OR)2.7; 95% CI)1.1-6.8). The use of flea and tick control products was unrelated to risk of CML. The authors concluded that the results from this study suggest that use of some lawn care chemicals may increase the risk of CML. Additional analyses are needed to evaluate whether specific chemicals in these products may be related to risk of CML, and perhaps to human NHL as well.