One hundred fourteen cases of post term pregnancy were clinically analyzed and classified. 1. In case of primipara, the duration of labor was longer and the frequency of prolonged labor (greater than 24 hours) was higher than that of the same number of cases of term delivery at 39 weeks. 2. The main cause of prolonged labor was weak pains. 3. The mean newborn umbilical artery pH in prolonged labor cases was not lower than that in other cases. 4. The cases of post-term pregnancy were classified into 4 groups and compared each other in several respects. Group I: prolonged labor(-), fetal distress(-), vaginal delivery. Group II: prolonged labor(-), fetal distress(+), vaginal delivery. Group III: prolonged labor(-), fetal distress(+), cesarean section. Group IV: prolonged labor(+). 1) The length of the fundus uteri: Group III: minimum after 31 weeks: Group IV: maximum after 35 weeks. 2) The body weight of the newborn and the weight of the placenta: Group III: minimum: Group IV: maximum. 3) The titer of E3 in urine: Group III: obviously low. 4) The frequency of Clifford's sign: Group III: high frequency of meconium staining. Cases of post-term pregnancy were composed of several groups with different clinical features.