SUMMARYA sample of 237 twin birthB drawn from the records of a maternity clinic has been analysed with regard to birth weight, gestation time, maternal age, parity and survival. The sample was divided into like‐ and unlike‐sex groups. The like‐sex twins have higher mean birth weight and length of gestation with lower mother's age and parity. The correlation of birth weight is 0–765 for like‐sex and 0–792 for unlike‐sex twins. The correlation between male and female twin pairs is 0–826. The number of monozygotic twins in this sample is estimated to be 81 and the estimated weight‐weight correlation for these is 0–815. Comparison has been made possible with similar data on English and Italian twin births published by Karn. The influences of the variables on the survival