A review of the literature on the validity and reliability of survey data is presented prior to an analysis of the reliability of selected questions in the Second Followup Questionnaire of the National Longitudinal Study of the High School Class of 1972 (NLS). The reliability study includes an evaluation of test-retest reliability as a function of data collection procedures (whether mail-in or personal interview), item characteristics (response format, item content, and item length), respondent characteristics (sex, ethnicity, socioeconomic status, and academic ability), and the interaction of these diverse factors. At issue is not only the quality of NLS questionnaire data, but the consideration of guidelines for analyzing survey data and improving the quality of that data. In lieu of an empirical analysis of validity that might have encroached on the privacy of respondents, the validity check was based on a literature review, focusing on NLS types of items. The validity study also focused on data collection procedures, item characteristics, respondent characteristics, and their interactions. An overview of the purpose of the NLS and the methodologies employed are also included. The Short Form of the Second Follow-up Questionnaire is appended. (Author/EVH)