The chief executive of Tonga's Ministry of Health says the Apollo hospital group has been receiving referrals from Fiji for the past six years and from Samoa over the last year.
Dr Siale 'Akauola said a Tongan medical team visited the hospital in India before the new agreement was signed.
He said the deal was an affordable option for Tonga.
"So far we have sent some patients already and we have looked at the initial reactions from the patients and we were very pleased with what they had experienced. We were a bit concerned about the long trip because it involves stop overs, so we select patients who can go there based on their ability to travel long hours on the plane," he said.
Dr 'Akauola said so far patients needing neurosurgery, cardiac surgery and cancer treatment had gone to India.