Thousands were taken captive during the war
A group of 59 Iraqi prisoners held since the 1980-1988 Iran-Iraq war has been freed in what the Red Cross says is likely to be the last such release.
The International Committee of the Red Cross says 70,000 people are still missing following the war, which left about a million dead overall.
But a spokeswoman said the agency had no reason to believe that Iran was holding any more Iraqi prisoners of war.
Monday's release was the first release of prisoners since March, when more than 1,000 detainees were exchanged.
The group flown to Baghdad on Monday included some people in poor health, the ICRC's Nada Doumani said.
She said that their families did not meet them.
Following the US-led war in Iraq, few people have working telephones, and the ICRC is now trying to contact family members.
The aid organisation says it has helped repatriate some 97,000 prisoners since the end of the war 15 years ago.
The issue of prisoners of war was a major obstacle to normalising relations between Tehran and Baghdad for years, with each country accusing the other of concealing how many prisoners it holds.
About one million people died in the eight-year war
Under an agreement reached in March, 941 Iraqi prisoners of war being held in Iran and 349 Iranians returned to their respective countries.
Each country said that would be the final exchange to take place, although Iran has said the file of those missing in action would remain open.
Iraq under Saddam Hussein denied the existence of Iranian prisoners of war, calling them common criminals instead.
Around a million people were killed in the war, with thousands of prisoners captured on both sides.
The issue of POWs is not the only reason why many in Iran feel bitter, the BBC's Miranda Eeles in Tehran says.
Thousands of people continue to suffer from the effects of chemical weapons used by Iraq during the conflict.
There is also a strong feeling in Iran that Iraq should pay compensation for the damage that it caused, estimated at billions of dollars.