BackgroundYouth may engage in healthy weight control behaviors (HWCBs) and unhealthy weight control behaviors (UWCBs) to lose or maintain weight. Youth observation of WCBs by supporter groups (parents/siblings/peers) and youth beliefs about the safety of WCBs may impact which WCBs youth use. The primary aim of this study was to examine the mediating role of youth safety perceptions of WCBs on the relationships between supporter group engagement in WCBs and youth engagement in WCBs. Youth BMI-z-score was analyzed as a moderator. MethodsParticipants were 219 youth (52.1% females), ages 10–17, attending an outpatient medical appointment. Participants completed questionnaires about their WCB use, whether they perceived WCBs as safe/unsafe, and whether they perceived parents, siblings and peers to use WCBs. A standardized formula including youth age, sex, height, and weight was used to calculate BMI-z-score. ResultsA moderated mediation model examining parental and youth engagement in UWCBs revealed that for youth in the healthy to overweight/obese (OV/OB) range, greater safety perception of UWCBs mediated the relationship between higher parent engagement in UWCBs and higher youth engagement in UWCBs. Furthermore, youth safety perception of HWCBs mediated the relationship between perceived parent, sibling, and peer engagement in HWCBs and youth engagement in HWCBs. ConclusionThis study identifies perceived parent, sibling, and peer WCBs and youth safety perceptions as mechanisms affecting youth WCB engagement, particularly for youth in the OV/OB range. Intervention effectiveness may increase if parent, sibling, and peer WCBs are targeted and education about safe/unsafe ways to control weight is provided.