The supine hypotensive syndrome occurs when the parturients near term in supine, enlarged uterus compresses the inferior vena cava and partially obstructs the lower aorta and venous return to the heart and arterial blood flow to the pelvic organs and lower extremities are decreased. Major supine hypotensive syndrome was defined as a fall greater than 30% or a value less than 80mmHg in systolic blood pressure. Many studies in Western countries have reported that up to 50% of parturients near term develop signs of shock including fainting, nausea, vomiting, loss of consciousness or sudden death when they assume supine position. The haxards of obstruction the aorta by the gravid uterus in pregnancy are well documented. Compression of the aorta is not associated with maternal symptoms but does cause arterial hypotension in the lower extremities and uterine arteries, so it can cause fetal distress and asphyxia. Most parturients are able to compensate for mild to moderate dupine hypotensive syndrome by increase in collateral circulation via azygos venous system and vertabral venous system and peripheral resistance or heart rate. But the anesthesiologists must recognize the importance of the supine hypotensive syndrome and the potential hazard of anesthesia in augmenting its effects. We have investigates the incidence of supine hypotensive syndrome in 171 parturients were Cesarean sectioned. We have investigated the correlating factors such as fetal body weight and parturient's physical status, body weight and age among the 36 cases of decreased blood pressure in supine position and also we have investigated the relationship between blood pressure changes and parturient's associated diseases. We have measured the arterial blood pressure indiredctly by the Rira-Rocci method when they are lying on the operating table in supine and compared it with arterial blood pressure in their comfortable position in ward. The results are as follows: 1) Among the 171 parturenits, the incidence of decreased arterial blood pressure in supine position was 21%(36casese). However the incidence of increased arterial blood pressure in supine position was 79%(135 caese). No case of severe blood pressure changes defined as a fall greater than 30% was notice but there was one case with less than 80 mmHg in systolic blood pressure which would be a rate of 0.6%. 2) The realationship between decreased blood pressure in supine posction and fetal body weight and parturient's physical status, body weight and age was not statistically significant(p>0.05). 2) The relationship between decreased blood pressure in supine position and parturient's associated diseases especially preechlampsia or eclampsia was statistically significant (p<0.05).