An investigation of the correlation of the placental weights of 500 unselected live-born babies delivered after a gestation period of 33 weeks at the minimum and 42 weeks at the maximum, respectively, with age, family status parity, and mother's occupation, as well as with the weight, maturity, and sex of the neonates yielded the following results: 1. Between primiparae, secundiparae, and multiparae, working and housewife mothers, workers, farmerettes, women doing other jobs, and academically trained women, eutrophic mature and hypertrophic mature neonates, and newly born male and female babies there was observed a roughly similar frequency of the generally accepted "normal weight of placenta" of 400 g to 600 g and no significance of minor differences in frequency, respectively. 2. The high incidence of mothers aged 20 and less in the "normal placental weight group" of 400 g to 600 g compared to 21- to 30-year-old and 31- to 35-year-old mothers was not found to be significant. 3. The high incidence of unmarried mothers in the "normal placental weight group" of 400 g to 600 g compared to married mothers is not significant, the higher incidence of premature labor in unmarried women being due possibly, not to the weight of placenta, but rather primiparity, age under 20, and social class. 4. The higher frequency in the placental weight group up to and including 400 g of married compared to unmarried mothers, primiparae compared to secundiparae, primiparae and secundiparae compared to multiparae, working mothers compared to housewife mothers, and workers and farmerettes compared to both women doing other types of jobs and academically trained women was not found to be significant.