Among the approximately 1,000 survivors of those blasts now living in the U.S. and Canada, dozens in Washington state are helping doctors help others.
Fred Hasegawa is one of those survivors - and he remembers the day vividly.
He was 15 years old, waiting for a train outside Hiroshima, when the atomic blast knocked him off his feet. He was far enough away to survive without injuries.
"All of a sudden, like lightning," he remembers. "The whole sky was a yellowish color. ... After the explosion I went through Hiroshima City - about four hours after the explosion."
People in 1945 knew nothing of radiation and its potentially ravaging effects on the human body many years after exposure.
Now, 68 years later, Fred is among hundreds of Japanese Americans who volunteer to undergo annual medical exams as part of a long-term study on the after-effects of radiation.
"So I try contribute my time and effort to help other people," he says.
For more than three decades, a team of doctors from Japan has traveled to Seattle to conduct the exams on survivors living in this country. It can be helpful to share in one's native tongue.
Doctors at Seattle's Pacific Medical Centers host the project - and collaborate.
"Opening up to the Japanese and saying there have been some tragic outcomes to this, but we want to help," says Dr. Vik Dabhi, chief medical officer at Pacific Medical Centers.
Fred is healthy - as he was before that fateful day. But he knows there are others who are not as fortunate.
"Myself, I don't need this help - but there are lots of other victims that need the help."