Obesity represents a well-known risk factor for renal cell carcinoma development. Several studies evaluated the relationship between obesity and outcome in patients with non-metastatic and metastatic renal cell carcinoma using different parameters such as BMI, visceral fat area and s.c. fat area. These studies suggest that obesity is associated with a better prognosis in renal cell carcinoma patients. This phenomenon is called obesity paradox and it was found in other diseases in which obesity represents an established risk factor such as heart failure, diabetes, atrial fibrillation, hypertension and coronary heart disease. The purpose of this review is to analyze the mechanisms by which obesity increases the risk of renal cell carcinoma development, to describe the evidence available to date about the link obesity-outcome and to evaluate the mechanisms to explain this apparently paradoxical relationship.