Tailored behavior change programs have proven effective at decreasing health risk factors, but the impact of such programs on participant well-being has not been tested. This randomized trial evaluated the impact of tailored telephone coaching and Internet interventions on health risk behaviors and individual well-being. Exercise and stress management were the primary health risks of interest; improvements in other health risk behaviors were secondary outcomes. A sample of 3391 individuals who reported health risk in the areas of exercise and stress management were randomly assigned to 3 groups: telephonic coaching that applied Transtheoretical Model (TTM) tailoring for exercise and minimal tailoring (stage of change) for stress management; an Internet program that applied TTM tailoring for stress management and minimal tailoring for exercise; or a control group that received an assessment only. Participants were administered the Well-Being Assessment and, at baseline, had relatively low well-being scores (mean, 60.9 out of 100 across all groups). At 6 months, a significantly higher percentage of both treatment groups progressed to the Action stage for exercise, stress management, healthy diet, and total number of health risks, compared to the control group. Both treatment groups also demonstrated significantly greater improvements on overall well-being and the domains of emotional health, physical health, life evaluation, and healthy behaviors. There were no differences between the groups for 2 well-being domains: basic access to needs and work environment. These results indicate that scalable, tailored behavior change programs can effectively reduce health risk and accrue to improved well-being for participants.