Obesity is the major nutritional problem affecting industrialised society. According to a recent ISTAT survey, 41% of men and 19% of women in the Italian population suffer from obesity. Obesity is a complex pathological entity with a multiform and often indeterminable etiology. Studies of natural and adopted children and twins suggest that a clear hereditary, constitutional predisposing factor is present in obesity which interacts with environmental conditions. The genetic factor is also suggested by the statistical finding that if neither parent is obese, then only 7-10% of their children will be obese, whereas if one parent is obese, 40-50% of children will probably become obese, and if both parents are obese as many as 70-80% of children will be obese. The risks related to obesity can be broadly categorised as mechanical and metabolic. The former include arthrosis, osteoporosis, degenerative diseases affecting the joints and bone matrix, muscular hypotrophy and respiratory deficits. The major metabolic risks include hypercholesterolemia, altered glycoregulation and hyperuricemia. From an obstetric point of view, apart from the fact that obesity is often associated with sterility, excess weight can often lead to sometimes dramatic complications during pregnancy, involving major risks for both mother and fetus. From a gynecological point of view the links between obesity, tumours and menopause are well known.