The purposes of the present study were to contribute additional data regarding the frequency of multiple births in Ankara, and to reassess both the relation between maternal age and twinning, and the inter-relation between twinning and seasonality. The frequency of twinning was found to be 0.0084858 +/- 0.00028 (0.85%), triplets 0.0001087 +/- 0.000031 (0.011%), and quadruplets 0.000009 (0.0009%). It is observed that there is a correlation between the frequency of twinning, maternal age and parity, and that the rate of twinning increases with maternal age. The twinning rate varies according to the month of the year in which birth takes place. Accordingly, the frequency of twin births is greater between May and August, and lower between September and December.