Around 187,000 women in Turkey are in polygamous marriages even though polygamy is illegal, according to a report seen by AFP on Tuesday.
The practice was found in the poor, Kurdish majority southeast as well as the industrialised west, said the study carried out by Hacettepe University in Ankara.
The report was presented last week to a parliamentary commission on equal opportunities.
It found that the majority of men in polygamous marriages had taken a second wife after their wife had been unable to bear a child, or, in particular, to have a boy.
More than seven million women in the secular nation of 73 million, which is overwhelmingly Muslim, had arranged marriages and nearly 5.5 million women were married before the legal age of 18, it added.
Turkey has stepped up reforms aimed at improving the lives of women in order to boost its chances of joining the European Union.
But feminist organisations say that much still remains to be done in order to tackle discrimination.