The objective of this study was to investigate the relationship between the accumulation of black dust matter in lungs (anthracosis) and primary lung cancer in dogs. A retrospective study was carried out on material from 35 dogs with primary lung cancer and 160 controls. The amount, histological appearance and birefringence of anthracosis were assessed in pulmonary specimens by light microscopy, and the odds ratio (OR) calculated for dogs with primary lung cancer. The same factors were analysed to identify an association between tumour histotype, histological grade, and clinical stage. Papillary adenocarcinoma was most commonly diagnosed (45.7%). The majority of tumours were of histological grade II, and the lung cancer was more often localised (clinical stage I). An increased risk of lung cancer was observed in dogs with higher amounts of anthracosis (OR: 2.11, CI 95%: 1.20-3.70; P < 0.01), which suggests an association between anthracosis due to inhalation of polluted air and lung cancer in dogs.