Previous studies have shown that active consent procedures result in sampling bias in surveys dealing with adolescent risk behaviors such as cigarette smoking and illicit drug use. To examine sampling bias from active consent procedures when the survey topic pertains to childhood obesity and associated health behaviors, the authors pair data obtained from both active and passive consent procedures. The authors find that parents of children who are overweight or at risk for being overweight are significantly less likely to give active consent. In addition, parents of children enrolled in lower grades are more reluctant to consent to participate. (Contains 3 tables and 2 notes.)