Mr McCain, who is running neck and neck with George W. Bush for the Republican presidential nomination in New Hampshire, had been the subject of a whispering campaign that has suggested he could have suffered long-term psychological damage from the five years he spent in a Vietnamese prisoner-of-war camp.
Mr McCain's supporters believe that the rumours, which developed out of reports from his home state of Arizona about his hot temper, were orchestrated by one or more of his Republican rivals. The suggestions started to circulate in late October, just as Mr McCain emerged as the strongest challenger to Mr Bush.
The records, as released to the Associated Press news agency at the weekend, showed that the most threatening medical condition to affect Mr McCain was skin cancer, in the form of a cancerous mole that was removed from his shoulder six years ago. The physical injuries he sustained during his capture and torture in Vietnam 25 years ago have left him with arthritis in his shoulders and one knee, which could require joint replacement in the future. "Otherwise," his doctor, John Eckstein, wrote, "I found you to be in excellent heatlh."
Successive reports on his mental state after he was released from the PoW camp in 1973 said that he had suffered no ill effects. "Patient's mental status has not been influenced by recent situational stress," said a report written shortly after his release. Another said: "There is no sign of emotional difficulty." IQ tests showed above average intelligence, and medical reports established a high pain threshold.
In making public his records, Mr McCain honoured a promise he had given four weeks ago, but the timing of the release was calculated to reap the maximum political benefit.
Tonight, Mr McCain will participate in the latest Republican candidates' debate, which takes place in his adopted home state of Arizona. In the most recent debate, held last week in New Hampshire, Mr McCain came out as the acknowledged winner, not least because he responded to persistent questioning about his temperament with good grace and humour.
Tonight, pleading previous engagements on the other side of the country, Mr McCain will be the only candidate not present in person and will take part in the debate via a satellite link. This could put him at a disadvantage against the other five candidates, including Mr Bush.
The release of his medical records, however, could not only defuse questions about his own state of health, but put pressure on the other candidates to follow his example.
This could place Mr Bush in an especially difficult position. He has never completely answered questions about drug use in his past - and never released his own medical records in two successful runs for the governorship of Texas.