Background: Healthy Dads Healthy Kids (HDHK) is a unique lifestyle obesity intervention for fathers and children that demonstrated weight loss among the fathers and behavior change among fathers and children in Australia. The program is gender-tailored to specifically target fathers for weight loss and 5-12 year old children for obesity prevention. The aim of this formative study was to examine an Expert Panel's and Hispanic Family Panel's perceptions about the program and suggestions for the cultural adaptation of HDHK for Hispanic families in southwestern US. Methods: Forty-four Hispanic participants (22 fathers, 13 mothers and 9 children) made up the Family Panel. They participated in 1-5 study contacts (focus groups, online survey, and/or interviews). The scripts and qualitative guides assessed participants' perceptions of the HDHK content and material using the Ecological Validity Model. Studies were conducted in English or Spanish, depending on the preference of the participant. Focus groups and interviews were audio-recorded, transcribed, translated, and thematically coded. Findings were reviewed with the Expert Panel who helped inform the cultural adaptation. Results: 80% of parents were foreign-born, 57% spoke only Spanish at home, and 60% did not graduate from high school. Several themes emerged to inform the cultural adaptation of the program. Parents agreed with the HDHK goals and recommended the program place greater emphasis on parenting and limiting children's screen time. Some mothers and fathers wanted greater mother engagement. Weekly videos and a Facebook group emerged as favorite alternative options to engage mothers. Greater promotion of familism (inclusion and impact on whole family) was recommended for the program goals and activities. Gender roles for mothers and fathers, and differences in how fathers interact with male and female children, emerged and should be considered in program activities. Several barriers to father engagement surfaced, including lack of time due to work schedules, physically demanding jobs, concerns of caring for children without mother, fathers' current fitness/weight, and lack of knowledge of how to eat more healthfully. The reading level of the HDHK materials was too high for some parents. Conclusion: Findings from these formative qualitative studies informed the cultural adaptation of HDHK for Hispanic families, to account for literacy level, cultural values, and barriers to participation and engagement.