OBJECTIVES: Obesity is considered a major Public Health issue in most developed countries nowadays for its wide spread across population groups, as well as its contribution to the development of chronic diseases. Our objective was to estimate and better understand the impact of progressively increasing Body Mass Index (BMI) on diagnosed Diabetes, Heart Attack (HA), Hypertension, Chronic Anxiety (CA) and Chronic Depression (CD) in adult population. METHODS: Retrospective analysis of the Spanish 2009 European Health Survey System data base was conducted. Data from population under 18 years old or with BMI under 18.5 or with not reported BMI were excluded. Sample size of 19,880 adults (89.6% of the initial sample) was available for analysis. A logistic regression model was constructed for each of the five dependent variables. Age groups were divided by quartiles. BMI groups were “18.5–24.9”, “25–29.9”, “30–34.9” (g3) and “35 or more”(g4). RESULTS: Diabetes prevalence was 7.7%; (OR adjusted for g3 :2.3; 95% CI: 2.0–2.7; OR_g4: 4.2; CI:3.4-5.3), Hypertension prevalence was 23.6%; (OR_g3: 3.4; CI:3.0–3.8; OR_g4: 5.8; CI: 4.8–6.9), HA prevalence was 2.8%; (OR_g3: 1.7; CI: 1.3–2.1; OR_g4: 1.6; CI: 1.1–2.5), CA prevalence was 8.2%; (OR_g3: 1.6; CI: 1.3–1.8; OR_g4: 2.3; CI: 1.8–2.9), CD prevalence was 7.9%; (OR_g3: 1.7; CI: 1.4–2.0; OR_g4: 2.7; CI: 2.2–3.4). All the stated OR reached statistical significance (p<0.05 for OR_g4 in HA and p<0.001 for all the rest of them). CONCLUSIONS: The results show how the risk of the examined comorbidities largely increases in those patients with BMI>35. Considering its potential economical impact on Public Health, it would be required to design and implement effective strategies aimed at the early detection of subjects at risk and the provision of adequate treatment, as well as to establish suitable preventive programmes.