Thirty-one hotels employing 11,000 persons on the island of Oahu are pair-matched. One member of each pair is assigned to a high intensity intervention and the other to a low intensity intervention. Both interventions are intended to reduce BMI through an emphasis on a healthy diet and increased physical activity. All employees are assessed annually for three consecutive years. The assessment includes a survey on lifestyle habits, stage of change, and attitudes toward weight, as well as measurement of BMI. The high intensity intervention hotels receive the following: 1) environmental changes to support lifestyle change and obesity control; 2) worksite based groups that offer state-of-the-art behavioral interventions; and 3) after-hours "Re-Invent Yourself" groups designed for persons who want to lose at least 25 pounds and are highly committed to doing it. These interventions incorporate all the elements that produce sustained weight loss and an innovative decision tutorial based on decision theory. The primary outcome is the mean difference between hotels in the high intensity and low intensity interventions in change in BMI from baseline to 12 and 24 months. Secondary outcomes address effects of the intervention on ethnic and occupational subgroups stage of change, absentee days, and worker compensation claims.