As reported by Censor.NET citing The Associated Press, Przemyslaw Walesa, 43, was found dead in his apartment in the northern city of Gdansk by a family member.
Gdansk police spokeswoman Aleksandra Siewert told the AP only that a body of a 43-year-old man was found by a relative in an apartment. She declined to identify the man at this early stage of proceedings.
Siewert said forensic experts, who were called to the site by an ambulance crew, had preliminarily excluded the possibility of someone contributing to the death. An autopsy was planned for Monday.
Przemyslaw was the third of Walesa's eight children - four sons and four daughters. In his youth he had problems with alcohol and with drunken driving.
Siewert told the AP that the victim had been previously noted by the police.
Lech Walesa, 73, won the Nobel Peace Prize in 1983 for his role in leading the nationwide Solidarity freedom movement. He was Poland's first popularly elected president, governing in 1990-95.