This exploratory study aimed to assess obesity, physical activity, and nutrition among Pacific Islander youth and young adults in Southern California. A total of 129 Tongan, Samoan, and Marshallese participated in the study, including relatively similar proportions of males and females and age groups. We calculated Body Mass Index (BMI), dietary intake by a food frequency questionnaire (FFQ), and 7-day physical activity levels with accelerometers. Overall, 84% of Tongan, 76% of Samoan, and 24% of Marshallese participants were overweight or obese, with mean BMI of 31.2 and 34.3 kg/m2 (for Tongan males and females), 32.3 and 33.4 kg/m2 (Samoan males and females), and 25.3 and 22.1 kg/m2 (Marshallese males and females). We found moderate- and vigorous-intensity physical activity (MVPA) fell below current guidelines at 38 min/day, with over 87% engaging in light-intensity PA and large sedentary times. Daily percent of energy from saturated fat, fiber/1,000 kcal and dairy intake were higher in Tongans compared to Samoans and Marshallese. Despite promising outcomes from this study, high prevalence of overweight, low physical activity levels, and high caloric intake put Pacific Islander youth and young adults at risk for a variety of health concerns and future efforts should focus on further research as well as community-wide prevention and amelioration efforts.