Obesity is a disease with severe health consequences and increased risk of mortality. The most commonly used criteria to assess the presence and the severity of obesity are body mass index, waist circumference, waist-to-height ratio and the presence of the health conditions caused or worsened by obesity. Worldwide obesity has more than doubled in the last 4 decades. Obesity is the second of the leading preventable causes of death worldwide (after smoking). Obesity has a plurifactorial pathogenesis. The central perturbation consists in the imbalance between calories intake and calories consumption (by inappropriate diet and sedentary lifestyle). Identification of all the ethiological factors is important for treatment and prophylaxis. Weight loss benefits are multiple and important: improvement in glicemic control and in plasma lipid levels, blood presure control, obstructiv sleep apneea reduction, improvement in management of daily activities and profesional performances, increase quality of life, reduction in mortality. Overweight or obese patient will complete a diagnostic and a treatment program. Treatment of obesity claims a targeted multidimensional therapy: weight and lifestyle management, diet, sustained physical activity in daily life, exercise, decrease life stressors, smoking cessation, drug therapy, bariatric surgery psichological, familial and social suport. Weight loss program must be carefully planned, adapted to the patient’s abilities and comorbidities and supervised by a nutritionist and a physiotherapist.