The reliability of the Behavioral Risk Factor Surveillance System questionnaire was assessed in a random sample of adults (n = 122) and a separate sample of Black and Hispanic adults (n = 200) in Massachusetts. The questionnaire was administered twice, 21 to 44 days apart, by telephone (210 completed reinterviews, 65% response rate for second administration). There were no statistically significant differences in the distribution of demographic or risk factor variables across administrations. Individual-level reliability (kappa for categorical variables, correlation for continuous variables) for demographic characteristics was more than 0.80 for White respondents and more than 0.60 for Black and Hispanic respondents. Employment and income were reported less consistently than other variables. Reliability coefficients for behavioral risk factors were generally above 0.70. Exceptions were variables with extreme distributions. These data support the use of the Behavioral Risk Factor Surveillance System questionnaire for surveillance and research.