The aim of this study was to assess the prevalence and clinical significance of fetal tricuspid valve regurgitation. In a cross-sectional study, 289 normally grown singleton fetuses with normal heart anatomy, normal estimated weight for gestational age, normal amniotic fluid volume and normal flow velocity waveforms in the umbilical and middle cerebral arteries and umbilical vein were examined. A further 31 singleton fetuses with intrauterine growth retardation (estimated fetal weight below the 3rd centile) were analyzed. Semiquantification of the tricuspid valve regurgitation by spatial and temporal parameters was performed in the four-chamber view by color Doppler flow imaging and by color Doppler M-mode echocardiography (M-Q mode). The prevalence of fetal tricuspid valve regurgitation among normally grown fetuses was 6.23% (n = 18). In all cases, the tricuspid regurgitation was part-systolic (non-holosystolic, early and mid-systolic tricuspid regurgitation) and showed little spatial expansion of the jet as examined by color Doppler flow imaging (no jet reached the opposite atrial wall, the area of tricuspid regurgitation being less than 25% of the atrial area). The maximum velocity of the regurgitant jets was below 2 m/s with one exception. There was no statistically significant correlation between gestational age and occurrence of tricuspid regurgitation (U test, p > 0.05). Re-examination of 14 of the 18 fetuses with tricuspid regurgitation showed that tricuspid regurgitation was a transient phenomenon in these instances. The fetal outcome in the presence of tricuspid valve regurgitation was normal. Regurgitations of the mitral, pulmonary and aortic valves were excluded in all 289 fetuses. Only two of the 31 fetuses (6.45%) with intrauterine growth retardation showed tricuspid valve regurgitation. In one fetus the tricuspid regurgitation ws only part-systolic. In the other severely compromised fetus with highly abnormal flow velocity waveforms in the arterial and venous side of the fetal circulation, cardiac dilatation with holosystolic tricuspid and holosystolic mitral regurgitation occurred immediately before intrauterine death. Fetal tricuspid valve regurgitation was a frequent finding during Doppler echocardiography. Although it may be a sign of increased preload, afterload or cardiac dysfunction, in most cases tricuspid valve regurgitation is an isolated transient finding with little temporal and spatial expansion, and it may be physiological.