Hemangiosarcoma was diagnosed in 104 dogs. The mean age was 10 years. Twenty-two breeds were represented. The most common were the German Shepherd Dog and Poodle. Most tumors were in the spleen (65/104). Other primary sites included the soft tissues of the trunk and extremities (18), liver (6), heart (3), and lung (2). Sixty of the dogs were examined because of rupture of the primary tumor or metastatic disease. Of the 104 dogs, 4 are alive and 100 are dead: 35 were euthanatized at the time of diagnosis, and the remaining 65 had a mean survival time of 123 days. The mean survival time of the 4 living dogs was 360 days. Forty-seven of the 65 dogs with splenic hemangiosarcoma were treated with surgery alone, surgery and immunotherapy, or surgery, immunotherapy, and combination chemotherapy. The same 47 dogs were clinically staged. There was no difference in survival time according to therapy or stage of disease.