OBJECTIVES: PRospective Obesity Cohort of Economic Evaluation Determinants (PROCEED) is an ongoing longitudinal cohort of overweight subjects aged 35-75 intending to lose weight. The primary objective is to compare health care consumptions and costs in subjects who are overweight (BMI 25 kg/m2) with or without abdominal obesity (AO) (waist circumference 102 cm for male and 88 cm for female) versus non-overweight subjects (BMI 20-24 kg/m2). METHODS: Recruitment started in the US in November 2004. Internet-based follow-up assessments will occur monthly for weight and waist circumference of overweight subjects, and quarterly for health and economic outcomes (hospitalizations, ER, outpatient services, prescription medications for selected conditions) of all subjects. RESULTS: Baseline analysis was conducted on non-overweight subjects (100) and overweight subjects with waist circumference measurement (293 without AO and 674 with AO). Health care resource costs per participant were calculated by applying unit costs to health care resource consumption reported at baseline during the past 3 months. Mean costs in overweight subjects with AO were almost twice those in overweight subjects without AO ($132 versus $72), and over 3.5 times those of controls ($37). Overweight subjects with AO compared with those without AO were more likely to have reported current prescriptions for depression (21.1% versus 12.3%) and diabetes (11.9% versus 4.4%). The percentage of subjects with zero costs was 23% and 31% in the overweight group (AO and non AO, respectively) compared with 39% in the control group. CONCLUSION: Abdominal obesity appears to be associated with markedly increase costs, especially those related to prescriptions. As the PROCEED cohort progresses, further collection and analyses of economic outcomes will allow a deeper understanding of the impact of abdominal obesity on costs and health care consumptions.