OBJECTIVE: To assess the effectiveness of a tailored theory-based, Web-delivered intervention (Young Adults Eating and Active for Health) developed using community-based participatory research process. DESIGN: A 15-month (10-week intensive intervention with a 12-month follow-up) randomized, controlled trial delivered via Internet and e-mail. SETTING: Thirteen college campuses. PARTICIPANTS: A total of 1,639 college students. INTERVENTION: Twenty-one mini-educational lessons and e-mail messages (called nudges) developed with the non-diet approach and focusing on eating behavior, physical activity, stress management, and healthy weight management. Nudges were short, frequent, entertaining, and stage-tailored to each behavior, and reinforced lesson content. MAIN OUTCOME MEASURE: All participants were assessed at baseline, postintervention (3 months from baseline), and follow-up (15 months from baseline) for primary outcomes of weight, body mass index (BMI), fruit and vegetable intake (FVI), physical activity (PA), and perceived stress; and secondary outcomes of waist circumference, percent dietary fat, energy from sugar-sweetened beverages, servings of whole grains, self-instruction and regulation for mealtime behavior, hours of sleep, and stage of readiness for change for consuming 5 cups of FVI, completing 150 minutes of PA/wk, and managing stress on most days of the week. Demographics were collected at baseline. ANALYSIS: Chi-square analysis and mixed-models repeated measures analysis were performed to determine differences between experimental and control outcomes. RESULTS: There were no differences between experimental and control participants in BMI, weight, and waist circumference. There were small improvements in FVI (P = .001), vigorous PA in females (P = .05), fat intake (P = .002), self-instruction (P = .001), and regulation (P = .004) for mealtime behavior, and hours of sleep (P = .05) at postintervention, but improvements were not maintained at follow-up. At postintervention, a greater proportion of experimental participants were in the action/maintenance stages for FVI (P = .019) and PA (P = .002) than control. CONCLUSIONS AND IMPLICATIONS: Young Adults Eating and Active for Health is one of the first studies to use the community-based participatory research process of PRECEDE-PROCEED to develop a non-diet approach intervention. Although there were no differences between experimental and control participants in weight change or BMI, the intervention supported positive change in behaviors that may mediate excessive weight gain, such as increasing FVI and more healthful self-regulation mealtime behaviors immediately postintervention. Additional strategies to maintain the behavior changes need to be explored.