Placental site trophoblastic tumour (PSTT) is a very rare and unique form of gestational trophoblastic tumour, representing about 1-2% of all gestational trophoblastic tumours. Usually, the pattern is a slow growing nodule implicating the endometrium and myometrium, accompanied by abnormal uterine bleeding. Three ultrasound types of PSTT are described, but thereis no specific characteristic for diagnosis. We present the case of a patient with an atypical placental site trophoblastic tumour diagnosed two months after a caesarean scar pregnancy. In the presented case there are several particularities, such as the rapid growth and progression of the tumour, the limitation to the myometrium and the difficulty of the differential diagnosis and approach.