Proposals for the most radical changes in the medical card scheme for 30 years were made at the conference in Killarney.
The IMO presented a discussion paper which proposed that the GMS scheme be expanded to include an extra 200,000 people, increasing it by 6 per cent.
It said the remaining 60 per cent of the population would continue to pay privately to be treated by general practitioners.
Family doctors will discuss the document, which examined the implications of everyone having a medical card, at meetings around the State in coming months.
The report also recommended that people with chronic diseases, such as asthma, diabetes and cardiovascular disease which require constant monitoring, should be issued with a "care card" entitling them to specific medical care.
At political level, the document said, there was little enthusiasm for extending the medical card scheme to the entire population. It proposed a national patient registration scheme.
At present, patients are not registered, meaning that doctors are not in a position to identify their particular patients.
The document said it was highly probable that significant sections of the population were underserviced in terms of preventive and long-term care, especially those with chronic illnesses.
The report said a public/private mix would facilitate the development of a "truly national" GP scheme and would eliminate any hardship at the margins in terms of access to acute care.
The doctors effectively rejected motions calling for the introduction of a free GP service for the entire population.
Proposals for students and people under 21 years were also rejected.
A Dublin GP, Dr Cyril Daly, said the logic of free GP care for all was inescapable. He said that 2 1/2 million people were now relying on a GP service which had not changed since the Famine.
A Government which could afford free third-level education and "pay £30 million for a football pitch, surely could afford free healthcare for its population".
A Mayo GP, Dr Ken Egan, said there was already a free GP system being operated "by stealth" by the Government without doctors benefiting.
He said up to 90,000 people who had been unemployed could now keep their medical cards regardless of income.
Dr Egan, a former IMO president, said wealthy farmers, if they took early retirement under the farmers' retirement scheme, could also get free healthcare.
However, Dr Henry Finnegan, a Ballinasloe GP, said a state GP service had led to a crisis in the NHS in the UK.