Isolated fetal pericardial effusion is generally held to have a good prognosis. We report a study of seven cases identified from a total of 504 fetuses scanned and followed with serial fetal scans.Our results show that it was associated with a poor fetal prognosis in six of the seven pregnancies. Probably due to the high incidence of mid-trimester abortion and the association with other abnormalities only evident postnatally, this has not, hitherto, been reported. We would advocate close follow-up and a guarded prognosis when isolated pericardial effusions are found on fetal scans.