Obesity is rapidly becoming an emerging disease in developing countries due to the increasing westernization of societies and change in the lifestyle. The etiology of obesity is said to be multifactorial, with a combination of genetic and environmental factors. Literature has been extensively reviewed to provide a broad overview of obesity. Data for this review were obtained from original articles, review articles and textbooks. Internet search engines were also employed. The years searched were from 1993 to 2008. Obesity, classified in terms of the body mass index and the waist–hip ratio, has several associated co-morbidities such as diabetes mellitus, hypertension, degenerative osteoarthritis and infertility. In Nigeria, there is limited information on obesity. A literature review on obesity is necessary to improve the knowledge about obesity in developing countries, its prevention and its management.