Poles have begun voting in a parliamentary election that is expected to shift power from a centrist and pro-market party to a socially conservative and eurosceptic party that favours more welfare spending to help the poor.
Voting stations across the nation of 37 million people opened at 7am and are to close at 9pm.
Exit polls will be released when polls close, with official results due on Monday.
Opinion polls show the populist Law and Justice party holding a strong lead over the ruling party, Civic Platform, which has governed the country for eight years.
It is not clear if Law and Justice will win enough votes to govern alone or if it will need a coalition partner.