The share and number of illegitimate births have been increasing for a few years in
Poland. Reasons of this increase are similar to those in other countries. Liberalisation o f
sexual life and tendency to relationships based on common law are the main reasons.
Using data gathered and published by the CSO, the author presents influence of such
variables as: mother's age, father's age, sequence of births, mother's sources of living
for illegitimate births frequency.
The author tries to find causes of number increase of such births, specific for Poland.