When her father retired, they returned to Puerto Rico and settled down in Santurce, a San Juan barrio.

In 1972 she was accepted into the Biochemistry and Molecular Biology training program at Johns Hopkins University School of Medicine, and in 1978 she earned a Ph.D. degree there.

In 1978, Cintrón read a recruitment announcement for the first mission specialist positions in the Astronaut Corps while completing her PhD research.

[clarification needed] However, her academic credentials impressed NASA management and she was offered a position as a scientist.

In 2004 she was named "Chief of NASA's (JSC) Space Medicine and Health Care Systems Office", which she continues to hold.