The Vietnam Experience Study was a multidimensional assessment of the health of Vietnam veterans. From a random sample of enlisted men who entered the US Army from 1965 through 1971, 7924 Vietnam and 7364 non-Vietnam veterans participated in a telephone interview; a random subsample of 2490 Vietnam and 1972 non-Vietnam veterans also underwent a comprehensive medical examination. During the telephone interview, Vietnam veterans reported current and past health problems more frequently than did non-Vietnam veterans, although results of medical examinations showed few current objective differences in physical health between the two groups. The Vietnam veterans had more hearing loss. Also, among a subsample of 571 participants who had semen samples evaluated, Vietnam veterans had lower sperm concentrations and lower mean proportions of morphologically "normal" sperm cells. Despite differences in sperm characteristics, Vietnam and non-Vietnam veterans have fathered similar numbers of children.