The subject of this study was 38 cases of non-immune hydrops fetalis and 11 cases of fetal hydrothorax and/ or ascites (FH/A), a syndrome characterized by the accumulation of pleural effusion and/or ascitic fluid, without generalized skin edema, due to various etiologies, admitted to the obstetrics ward of Hokkaido University Hospital during the period between 1987 and 1994. Fetal treatment consisted of (1) intravascular transfusion or intra-abdominal transfusion for anemia, (2) frequent centesis or shunt insertion for pleural effusion and ascites, (3) reduction of cystic hygroma by puncturing and OK432 injection, and (4) intravascular or maternal injection with an anti-arrhythmic drugs to treat tachycardia. The outcome of NIHF and FH/A was assessed to be able to make a prognosis in NIHF and to compare the efficacy of fetal therapy in cases with (15 cases: 9 NIHF, 6 FH/A) and without (34 cases: 29 NIHF, 5 HF/A) intrauterine treatment. The average survival rates were 23.1% in NIHF and 54.5% in FH/A. None of fetuses with a chromosomal abnormality or cystic hygroma survived. The average GW at the time of detection of NIHF by ultrasonography was week 24.9 +/- 1.1 (mean +/- S.E., n = 38). The average GW at the time of detection of FH/A by ultrasonography was week 26.6 +/- 1.8 (n = 11). NIHF was detected significantly earlier in the IUFD and early neonatal death group (GW 22.4 +/- 1.4) than in the survivor group (GW 27.6 +/- 1.2) (p < 0.05). FH/A was also detected earlier in the IUFD/early neonatal death group than in the survivor group (GW 21.8 +/- 2.4 vs. 31.1 +/- 1.1, n = 11, p < 0.05). The survival rate in the intrauterine treatment group was higher than in the nontreatment group (treatment group: 10/15; non-treatment group: 5/34, p < 0.001). After the trial of intrauterine treatment in the 15 cases mentioned above, some efficacy was observed in 7 cases (reduction of cysts, effusion or edema, disappearance of arrhythmia).