Placental lakes are sonolucent or hypoechoic areas in images of the placenta, usually considered a physiological dilation of intervillous space with a rather good obstetrical outcome. However, diagnostic criteria for and the clinical significance of placental lakes are yet to be completely established, because of a wide variety of ultrasound findings, especially on color Doppler examination. We experienced a case of a huge placental lake, larger than the total placental area, located in an entire retroplacental space, concomitant with several penetrations of artery type blood flow. The antenatal differential diagnosis and course of clinical management are reported.