This paper reports on an atypical presentation of imperforate hymen. A case of silent massive hematocolpos in a 11-year-old girl mimicking as a giant ovarian cyst is described. The diagnosis was made after examination under anesthesia. Successful surgery was then performed. We conclude that hematocolpos should always be included in the differential diagnosis of cystic pelvic pathology in perimenarcheal girls even in the absence of clinical symptom of cyclical lower abdominal pain.