Study Abstract: In response to a legislative mandate, the VA initiated a survey entitled A National Health Survey of Persian Gulf Veterans and Their Families. The survey was designed as a retrospective cohort study in which the health of a population-based sample of 15,000 troops deployed into the Persian Gulf area was compared to those of 15,000 troops not deployed in the Persian Gulf area. The survey was to be conducted in three phases. In Phase I of the study, a structured health questionnaire was mailed to each of the 30,000 Persian Gulf War-era veterans who were sampled for the survey. Up to four follow-up mailings were sent to non-respondents to increase the response rate in a six-month period. In Phase II, telephone interviews of a sample of 8,000 non-respondents and a review of selected medical records for a sample of 4,000 veteran respondents were conducted. Through additional telephone interviews with non-respondents, the potential for non-participant bias was evaluated. The medical records review helped in assessing validity of selected self-reported health data (clinic visit, hospitalization, pregnancy outcomes, birth defects among children, infant deaths, etc.).