Dogs enrolled in a Swedish insurance company (during 1995–2006) were studied for development of pyometra and mammary tumours (MTs), with special attention to breed and age. There were over 260 000 female dogs with over 1 000 000 dog-years at risk (DYAR) in the database, using data on bitches up to 10 years of age and 110 breeds with over 1000 DYAR. In total, 20 423 bitches were diagnosed with pyometra and 11 758 with MTs and 30 131 with either or both of the two diseases. The incidence rate (IR) for pyometra was 199 (95% CI 196–202), for MTs 112 (95% CI 110–114) and for either or both of the two diseases 297 (95% CI 294–301) dogs per 10 000 DYAR. The mean age of diagnosis pyometra was 7.0 years (SD ± 2.2), MTs 8.0 years (SD ± 1.6). In all breeds, the overall proportion of the bitches that developed disease by 10 years of age was for pyometra 19%, MTs 13%, and either or both of two diseases 30%. The top 10 breeds diagnosed with either or both of the two diseases were the Leonberger (73%), Irish Wolfhound (69%), Bernese Mountain Dog (69%), Great Dane (68%), Staffordshire Bull Terrier (66%), Rottweiler (65%), Bullterrier (62%), Doberman (62%), Bouvier des Flandres (60%), Airdaleterrier (60%). These data provide information of the combined disease incidence in a large number of different breeds. Breed variations in incidence rate suggests genetic components in disease development. Our study may be valuable in the search for genetic risk-factors or protective factors.