Introduction: Changes in unhealthy lifestyles are key elements in the prevention and treatment of obesity and hypertension. Internet-based programs offer great potential for the implementation of evidence-based interventions focused on promoting healthy habits. We evaluate the efficacy of an Internet-based self-administered program ("Living Better") that addresses people diagnosed as being overweight or having type I obesity and hypertension. Methods: The sample was composed of a total of 106 participants (age Mean = 53; 59 males) from a public hospital in Spain, diagnosed as being overweight or having type I obesity and hypertension and randomized into two groups-the intervention group (IG; Internet-based intervention) and the control group (CG; usual medical treatment). The intervention used cognitive-behavioral strategies and psychoeducation to promote healthy habits. Anthropometric data (i.e., Body Mass Index-BMI-, waist circumference, and hip circumference) and lifestyle/psychological data (i.e., quality of life, physical activity, eating styles, motivation, mood, and self-efficacy) were assessed before and after the intervention, and at 6 and 12-month follow-ups. Results: Significant differences were observed between the IG and the CG in anthropometrical variables after intervention (i.e., BMI and waist circumference), external eating style, and anxiety and stress scores (p < 0.05). Follow-up data showed that changes were maintained in BMI, waist and hip circumference, and external eating in the IG. After receiving the Internet-based treatment, the CG also improved its clinical condition. Discussion: This study demonstrates that the Internet is a viable alternative for the delivery and dissemination of interventions focused on promoting healthy habits, and a totally self-administered intervention can produce long-term positive results. 1. Introduction Lifestyles are one of the most important determinants of health. Sedentary behaviors, consumption of fatty foods, fast food, tobacco, alcoholic beverages, stress, among other factors, are currently the most important causes of mortality and illness [1-3].