Mature cystic teratomas of the ovary are well recognized entity, which on occasion can cause an acute abdomen, when ruptured. A spontaneous rupture into transverse colon is a most unusual complication for a mature cystic teratoma of the ovary. The symptomatology can vary significantly, depending on the adjacent organs involved, and the diagnostic workup can be misleading. We present a case of a mature teratoma that caused a large bowel perforation.