At present, obesity and tumour diseases represent an important healthcare issue that has its socioeconomic and social dimensions. It has been known from literature for some time that certain types of tumours are more common in obese people than in people with normal body weight. About 3.2% of newly diagnosed cancers in men and 8.8% in women are associated with high body mass index (BMI). However, many studies suggest a more significant correlation between a waist-to-hip ratio (WHR) and a risk of cancer than a BMI. This is in line with the current orientation of knowledge not only to the quantity but mainly to the distribution of adipose tissue within a body with focus on metabolically active adipose tissue. Similarly, pathogenesis of cancers in obese patients is determined by a range of important mechanisms and metabolites such as insulin, insulin-like growth factors (IGFs), insulin resistance, inflammatory cytokines, adiponectin, leptin and many others. Despite this, many interconnections remain unknown. However, based on the results of many clinical and epidemiological studies we may argue that obesity is considered a risk factor of a number of tumour diseases such as prostate tumours, breast cancers in postmenopausal women, endometrial tumours, kidney or gastrointestinal tumours (stomach, oesophagus, colon).