One hundred and eleven users of IUD were recruited and classified into two groups. 40 cases were in the tailed group, and 71 cases in the tailless group. The samples ol each case were obtained from vaginal vault, the internal os of the cervix and uterine cavity. The cultures for detection of aerobic and anaerobic micro-morganisms were indentified.The results indicated that 11 cases were of positive test in the internal os samples. Among them 8 cases were in the tailed group and 3 cases in the tailless group. There was a very signilicant difference (P<0.01). 7 cases were found to be positive cultivation in the uterine cavity group among which 5 were in the tailed group and 2 in the tailless group. There was a signilicant difference (P<0.05).It is noteworthy that the increased incidence of bacteria ascending from the internal os to the uterine cavity was lound in the tailed group than that in the tailless group. However, severe pelvic inflammatory diseases in general have not been observed. One hundred and eleven users of IUD were recruited and classified into two groups. 40 cases were in the tailed group, and 71 cases in the tailless group. The samples ol each case were obtained from vaginal vault, the internal os of the cervix and uterine cavity. The cultures for detection of aerobic and anaerobic micro-morganisms were indentified.The results indicated that 11 cases were of positive test in the internal os samples. Among them 8 cases were in the tailed group and 3 cases in the tailless group. There was a very signilicant difference (P <0.01) .7 cases were found to be positive cultivation in the uterine cavity group among among 5 were in the tailed group and 2 in the tailless group. There was a signilicant difference (P <0.05). It is noteworthy that the increased incidence of bacteria ascending from the internal os to the uterine cavity was lound in the tailed group than that in the in tailless group. However, severe pelvic inflammatory diseases in general have not been observv ed.