Gen Wojciech Jaruzelski, Poland's last Communist leader, has been taken to hospital suffering from pneumonia, Polish media say.
The 87-year-old, who has suffered frequent health problems in recent years, was admitted to a police clinic in the north-eastern city of Olsztyn.
He is conscious and can talk to nurses, the daily Gazeta Wyborcza reports.
The general was recently put on trial by Poland's post-Communist authorities for imposing martial law in 1981.
Reports on Wednesday said he had been placed in the cardiology ward of the interior ministry hospital in Olsztyn, near his holiday home.
The Polish news agency PAP said he was in a stable condition and was expected to leave the hospital soon.
Last year, Gen Jaruzelski had surgery for a face tumour and the year before he was treated in hospital for pneumonia and heart problems.
The former leader maintains he imposed martial law in 1981 only to avert an invasion by Moscow, as the opposition Solidarity movement challenged Communist rule.
Dozens of people were killed during the crackdown and Gen Jaruzelski was put on trial along with eight other ex-officials in 2008 for the criminal use of martial law legislation.
Correspondents reported at the time that there seemed to be little public clamour in Poland to send the general to prison.
He made a public appearance in November when he was invited to a sitting of Poland's National Security Council by the current President, Bronislaw Komorowski.
Former presidents Aleksander Kwasniewski and Lech Walesa - Gen Jaruzelski's old foe from communist times - also attended the sitting.