The small-group Chronic Disease Self-Management Program (CDSMP) has proven effective in changing health-related behaviors and improving health statuses. An Internet-based CDSMP was developed to reach additional chronic-disease patients. We sought to determine the efficacy of the Internet-based CDSMP. We compared randomized intervention participants with usual-care controls at 1 year. We compared intervention participants with the small-group CDSMP at 1 year. Nine-hundred fifty-eight patients with chronic diseases (heart, lung, or type 2 diabetes) and Internet and e-mail access were randomized to intervention (457) or usual care control (501). Measures included 7 health status variables (pain, shortness of breath, fatigue, illness intrusiveness, health distress, disability, and self-reported global health), 4 health behaviors (aerobic exercise, stretching and strengthening exercise, practice of stress management, and communication with physicians), 3 utilization variables (physician visits, emergency room visits, and nights in hospital), and self-efficacy. At 1 year, the intervention group had significant improvements in health statuses compared with usual care control patients. The intervention group had similar results to the small-group CDSMP participants. Change in self-efficacy at 6 months was found to be associated with better health status outcomes at 1 year. The Internet-based CDSMP proved effective in improving health statutes by 1 year and is a viable alternative to the small-group Chronic Disease Self Management Program.