The Vietnam Era Twin Registry: a quarter century of progress.

Now celebrating its 26th year of existence, the Vietnam Era Twin Registry continues to be one of the largest national samples of adult twins in the United States. The Registry twin member population is composed of 7,369 US male-male twin pair Veterans (14,738 total individuals) who served on active duty in the military during the Vietnam conflict (1964-1975). The Registry also maintains a register, data repository, and a biospecimen repository.