CDC provides technical assistance to Porter/Novelli (Washington, D.C.) in conducting the HealthStyles Survey, an annual mail survey of health-related attitudes and behaviors in the United States. In 1999, investigators solicited 3,550 households that had previously indicated a willingness to respond to survey questions. This sample was selected as representative of the U.S. population on the basis of eight demographic variables: age, sex, marital status, race/ethnicity, income, region, household size, and population density. A total of 2,636 (74%) households responded; the 749 (28%) households with children aged 5-18 years were asked (1) if their youngest child walked or biked to school at least once a week during the preceding month, and (2) whether any of six specified conditions made it difficult to do so: traffic danger, crime danger, long distances, weather, opposing school policy, or other reasons. Respondents also had the option of stating that their children had no barriers to walking or biking to school. Results were weighted to match population distribution in the United States by using the eight demographic variables.