A case of polysplenia syndrome with atrioventricular (AV) block was reported. The case was diagnosed prenatally by using ultrasonography. The important findings for the diagnosis of this syndrome were discussed. (Case) A 30 year old para-1 housewife was observed in the 7th week of her second pregnancy during her first prenatal visit and was evaluated as an outpatient every 4 weeks thereafter at Totsuka Hitachi hospital. In the 27th week of gestation, a fetal bradycardia of about 50 bpm. was first pointed out and she was referred to our hospital. The ultrasonographic findings were as follows: (1) an artial septal defect (ASD) with an AV block, (2) a dilatation of the azygos vein parallel to the descending aorta, (3) an undetectable fetal spleen, (4) atresia of the upper intestine, and (5) no detectable abnormalities in the limbs. We diagnosed the fetus as polysplenia syndrome. She was admitted to Totsuka Hitachi hospital at the 33rd week of gestation because of a threatened preterm labor with ruptured membranes and she delivered an 1850 g female baby on the following day, despite being given a tocolytic agent. The infant died shortly after delivery. The autopsy showed polysplenia, ASD, azygos connection, and duodenal atresia; and the diagnosis of the polysplenia syndrome was confirmed. (Comment) We suggest that the following ultrasonic findings are important for the diagnosis of fetal polysplenia syndrome; (1) congenital heart disease with an AV block, (2) dilatation of the azygos vein, (3) visceral anomaly and an undetectable spleen, and (4) undetectable limb abnormalities which often indicate chromosomal anomalies.