Over a period of approximately 1 year, 2 sibling Rottweilers and their dam in the same household developed stage IV and stage III lymphoma, respectively. All 3 initially responded to doxorubicin chemotherapy but relapsed after approximately 3 months and were subsequently euthanased. As no obvious environmental trigger could be identified in these dogs, it is speculated that an underlying genetic predisposition could have played a role in the development of lymphoma in these related dogs.