OBJECTIVES: The obesity pandemic is driving an increase in healthcare utilization. However the specific breakdown of increased morbidity and associated usage requires linked primary care, chronic disease and hospitalization registries. Clalit Health Services (CHS), with its comprehensive stable database of over 4 million members, provides a strong base for comparing morbidity and health care utilization between obese and non-obese patients, thus laying the groundwork for informed health care policy. METHODS: We selected two random samples, 10,000 obese (BMI>30 1/Jan/2011) patients and 10,000 not-overweight (BMI<=25) from the CHS database aged 25-74, matching  CHS population age standard. We linked both datasets to the chronic disease registry, identifying the following diagnoses: diabetes, ischemic heart disease (IHD), congestive heart failure (CHF), hypertension (HTN), s/p cerebral vascular accident (CVA), chronic renal failure (CRF), and rheumatoid arthritis (RA).  We compared disease prevalence, hospital admission rates and total cost for the groups. RESULTS: The prevalence of all chronic disease The greatest effect was seen for diabetes (RR=3.39 CI 3.15-3.65), CHF (2.23 1.79-2.78), and HTN (2.34 2.22-2.46) but also for IHD, CVA , CRF and RA (1.77, 1.69, 2 and 1.37 respectively). Risk of hospitalization over three years was increased (1.34 1.28-1.42) and, on average, there were 58% increase in hospitalizations and 303% overall increased cost of healthcare compared to non-obese patients. CONCLUSIONS: The presence of obesity increases risk of severe comorbidities within the general population. Obesity increases risk of any hospitalization and both total cost and total hospital admissions among patients. Our findings suggest the need for intensive proactive health care policy to prevent and remedy obesity to prevent the financial collapse of over-stretched health organizations, and indicate the potential for cost-effectiveness of interventions,  whether behavioral, pharmaceutical, or surgical, or combinations thereof.