Obesity, defined as a body mass index ≥ 30 kg/m² in adults by the National Institutes of Health, is associated with an increased risk for a number of health conditions, including hypertension, unfavorable lipid level, and diabetes mellitus. During the past 2 decades of the twentieth century, the prevalence of obesity has increased in the United States. In 2009 to 2010, 36% of adults were obese, including 41 million women and > 37 million men. In addition, the prevalence of metabolic syndrome (MetS), which is a constellation of interrelated cardiac risk factors including visceral obesity, impaired insulin action (ie, insulin resistance), atherogenic dyslipidemia, endothelial dysfunction, and systemic inflammation, has been increasing in the United States. More recently, there has been greater interest in the effects of obesity and MetS on a variety of benign and malignant urologic conditions. Obesity/MetS has been shown to have an effect on urolithiasis; benign prostatic hyperplasia and lower urinary tract symptoms; female incontinence and pelvic prolapse; male hypogonadism; and male sexual function and infertility. These urologic diseases have a considerable impact on patients' quality of life. From a urologic cancer standpoint, obesity/MetS has been demonstrated to play a role in prostate cancer and in renal cell cancer; its role in bladder cancer remains ill defined. Furthermore, dietary or lifestyle modifications may improve outcomes in many of these urologic disease processes. Thus, it is imperative for physicians to understand these relationships in order to better screen obese patients and be aware of the potential impact of weight loss on affected benign and malignant urologic conditions.