The objective of this study is to compare between 2D and 4D Ultrasound in the detection of the causes of Oligohydramnios. A total 100 pregnant women with oligohydraminos were included in this study. The results showed that 6 cases (6.0%) had positive TORCH infection and the examined fetuses were abnormal in 36 cases (36.0%). Causes for oligohydraminos were detected in 37 cases (37.0%) and the most common detected cause was autosomal recessive polycystic kidney in 13 cases (35.2%) followed by bilateral multicystic dysplastic kidney in 8 cases (21.6%) and posterior urethral valve in 6 cases (16.2%) and obstructive uropathy was recorded in 4 cases (10.8%) however, 3 cases, 2 cases and 1 case was recorded for bilateral renal agenesis, Meckle Gruber syndrome and unilateral renal aplasia, respectively. The mean duration of examination was significantly higher in 4D compared to 2D. Thermal index was slightly lower in 4D while in contrary, mechanical index was significantly higher in 4D compared to 2D. In detection of fetal causes for oligohydraminos, the 2D ultrasound had a sensitivity of 94.6%, specificity of 100%, PPV was 100%, NPV was 96.9% and the accuracy was 98.0%. While, the 4D ultrasound had a sensitivity of 97.3%, specificity of 100%, PPV was 100%, NPV was 98.7% and the accuracy was 98.7%. In conclusion, both 2D and 4D US are equally effective in detecting causes of oligohydramnios but, the difference between the two procedures was not statistically significant "with a slight preference for 4D US".