A 5-y-old multiparous female common marmoset (Callithrix jacchus) presented with acute weight loss of approximately 25% over a 1-wk period. An abdominal mass was apparent on physical examination, and radiographs suggested peritoneal effusion. Exploratory laparotomy revealed hemoperitoneum and an enlarged, gray, hemorrhaging uterus; ovariohysterectomy was performed, and the marmoset recovered. Histologic evaluation of the ovaries and uterus revealed uterine rupture, with invasion of placental villi lined by trophoblasts through the myometrium to the serosal layer. Primary uterine rupture is a rare but serious obstetric event in humans and has been reported only rarely in NHP. This report is the first description of primary uterine rupture during early pregnancy in a common marmoset.