According to World Health Organisation estimates 1.1 billion people were overweight or obese worldwide in the year 2000 with the prevalence rapidly increasing. Compelling evidence suggests that excess body weight is a risk factor for several cancer types including cancer of the colon, breast, endometrium, kidney, oesophagus, as well as possibly additional sites. According to previous meta-analyses and systematic literature reviews, an important proportion of cancer has been estimated to be attributable to excess body weight. The extrapolation of a European meta-analysis  to the Swiss situation broadly estimates that around 700 cancers could be prevented in the absence of overweight and obesity in this country. The data presented highlights the public health relevance of preventing excess body weight. Several interacting metabolic and hormonal pathways seem to underlie the association between being overweight and cancer with insulin-resistance playing a central role. Since evidence is mounting that excess body weight can also adversely affect cancer prognosis, obesity is a primary target for cancer control programs.