We report the case of a patient with hematocolpos on hymenal imperforation, revealed following cyclic pelvic pain with primary amenorrhea associated with pelvic heaviness for one year. MRI showed significant distension of the vagina forming a pseudo mass, well limited, in T1 high signal, in moderate T2 high signal, with the presence of declining deposits in hyposignal related to hemosiderin. A hymenotomy was performed under general anaesthesia, the postoperative course was favourable. This case illustrates the particularity of suspecting a hematocolpos in the presence of a pelvic mass in a young girl with amenorrhea.  Kulcsszavak: hematocolpos, hymenal imperforation, amenorrhea, ultrasound, MRI