Background There is little information on which to base the prognostic counselling as to whether an antenatally diagnosed fetal abdominal cyst will grow or shrink, or need surgery. This study aims to provide contemporary data on prenatally diagnosed fetal abdominal cysts in relation to their course and postnatal outcomes. Methods Fetal abdominal cysts diagnosed over 11 years in a single centre were identified. The gestational age at diagnosis and cyst characteristics at each examination were recorded (size, location, echogenity, septation and vascularity) and follow-up data from postnatal visits were collected. Results Eighty abdominal cysts were identified antenatally at 28+4 weeks (range 11+0-38+3). Most (87%) were isolated and the majority were pelvic (52%), simple (87.5%) and avascular (100%). Antenatally, 29% resolved spontaneously; 29% reduced in size; 9% were stable and 33% increased in size. Forty-one percent of cysts under 20 mm diameter increased in size, while only 20% of cysts with a diameter of over 40 mm increased in size. The majority of cysts were ovarian in origin (n=45, 56%), followed by intestinal (n=15, 18%), choledochal (n=3, 4%), liver (n=2, 3%) and renal/adrenal origins (n=2, 3%), respectively. In 16% (n=13), the antenatal diagnosis was not obvious. Seventy-five percent of the cysts that persisted postnatally required surgical intervention. Conclusions Most antenatally diagnosed fetal abdominal cysts were ovarian in origin. Though most disappeared antenatally, nearly three quarters required surgical intervention when present after birth. Cysts of intestinal origin are more difficult to diagnose antenatally and often require surgery.