He was sentenced last week to seven years in prison, but U.S. Sen. Jim Webb met the country's military leaders and won his early release Sunday. Yettaw, who is in poor health, flew to Thailand later Sunday and spent two days undergoing tests in Bangkok hospitals.
Using a wheelchair and wearing a face mask, Yettaw said "Love you" to journalists before heading onto a flight in Bangkok on Tuesday morning. He made no other comments.
He was ticketed through to Springfield, Missouri, according to airline officials who spoke on condition of anonymity because they were not authorized to speak to the media.
Myanmar has said that Yettaw was freed on humanitarian grounds because of his health. He reportedly suffers from diabetes, epilepsy and asthma and was hospitalized for a week during his trial after suffering seizures.
Yettaw was apprehended May 6 as he swam away from Suu Kyi's lakeside residence, where he had sheltered for two days after sneaking in uninvited. He was convicted last week of breaking the terms of Suu Kyi's house arrest and related charges, and sentenced to seven years in prison with hard labor.
Suu Kyi, who has been detained for 14 of the last 20 years, was herself sentenced to three years in prison with hard labor for violating her house arrest conditions through Yettaw's visit, although that was reduced to 18 months under house arrest by order of junta chief, Senior Gen. Than Shwe.
Observers widely believe Yettaw's intrusion into Suu Kyi's home gave the junta a legal pretext to keep the Nobel laureate incarcerated through next year's general election. Yettaw testified that he had a vision that Suu Kyi was at risk from assassins, and visited her to warn her.
Webb, a Democrat from Virginia, on Saturday became the first U.S. senior political figure to meet with Than Shwe.
He also met with Suu Kyi, and said afterward that she appeared to be open to the idea of Western nations lifting some of the sanctions they have imposed on Myanmar's junta for its poor human rights record and for failing to relinquish power.
Suu Kyi has been known in the past to support Western sanctions against her country's government, although her precise position is difficult to discern because she has not been able to speak publicly since she was last taken into detention in May 2003.