Hemoperitoneum secondary to traumatic rupture of an adrenocortical adenocarcinoma was diagnosed in a 10-year-old male dog. Immediate surgical attention was required to remove the tumor and to control hemorrhage. The dog appeared to develop transient hypoadrenocorticism after surgery, but recovered with short-term exogenous corticosteroid administration. At 6 months after surgery, the dog was clinically normal.