Jeon Wook-pyo, 68, was among 25 fishermen aboard two boats -- the Five Oceans No. 61 and No. 62 -- who were abducted by North Korea Dec. 28, 1972, off South Korea's west coast.
Jeon escaped North Korea and was hiding in an undisclosed third country when he sent a letter to South Korean President Park Geun-hye, asking for help in returning home, Yonhap news agency reported.
"I took a chance to escape the North because I had a growing wish to spend the rest of my life with my relatives and brothers at home," Jeon wrote in the letter.
A government official, whose name wasn't reported, said "Jeon is now undergoing questioning."
Those abducted by the North are often used for propaganda or for intelligence gathering, Yonhap said.