The purpose of this study was to test the Let's Go 5-2-1-0 program delivered through motivational interviewing by nurses with 4-18-year-old overweight children and parents in primary care (PC). A quasi-experimental design allocated 60 control families to standard clinical care (SCC) and 70 families to SCC plus the 5-2-1-0 intervention. Drop-out rates were 9 and 35% at 6 months and 25 and 41% at 12 months, respectively for control and intervention participants. BMI percentile trended (p = .057) toward decline (M change = -3.0 versus -1.5) for intervention children at 6 months (n = 52 control, 44 intervention), and nonsignificantly (p = 0.14) for both groups (43 control, 40 intervention) at 12 months (controls -1.9, intervention -4.6). Intervention effects were found for self-reported daily fruit/vegetable consumption, physical activity, and screen time. Satisfaction was high. Further study of the PC nursing intervention is warranted.