In order to elucidate the pathogenetic factors of Ekiri, the author carried out the investigation of the pathogenetic factors from statistical viewpoint. The results obtained were as follows. 1) All cases of Ekiri patients studied here, 911 cases, were picked up from the Ekiri patients hospitalized into 19 isolation hospitals throughout the nation from July 1. 1954 to Sept. 30. 1950. The control group, having 739 cases, was picked up so as the constituting membership of the group to be identical with the patient group in age and sex. The body weight at birth was compared with each other group. 2) The proportion of members whose weight were less than 2,500 g. to the all members of respective group was about 2 times greater at the patient group than the control group, i.e. 11.8% for the former vs. 6.4% for the latter. 3) The mean value of frequency distribution against the body weight at birth was smaller on the patient group. On the other hand, the standard deviation was found to be great on this group. 4) The proportion of the members whose weight were less than 2,500g. was always large on the patient group regardless age, sex and district. 5) The occurrence of Ekiri among the children whose body weight were less than 2,500g. at birth was about 1.3~2.97 times higher than the average occurrence of that throughout the nation. 6) When Ekiri is thought as a kind of reaction occured on immature child, there may be brought a new aspect that can give us a new and helpfull recognition about the diathesis. the symptom, the manifestation and the pathology of Ekiri.