Obesity has become a pandemic disease causing a variety of lifestyle-related diseases, such as hypertension, dyslipidemia, diabetes mellitus, liver cirrhosis and hepatocellular carcinoma; therefore obesity has become an important health issue all over the world. Obesity was suggested to cause a chronic liver disease called nonalcoholic steatohepatitis (NASH) and to promote the progression of NASH to liver cirrhosis and hepatocellular carcinoma 30 years ago and this was proven 20 years ago. Today, 1% of the Japanese population is suffering from NASH. Twenty percent of NASH patients, 0.2 million patients, are suggested to develop liver cirrhosis latently in the next decade, and are at a serious risk of developing hepatocellular carcinoma. Indeed, diabetes mellitus has become prevalent among the Japanese population and 10% die from chronic liver disease, but few doctors are able to recognize liver cirrhosis and hepatocellular carcinoma in patients with diabetes mellitus. It is a serious health issue to ignore such risk factors that threaten life in Japan. There are many chronic liver diseases with fatty liver, and nonalcoholic fatty liver disease (NAFLD), a chronic liver disease of unknown etiology, affects 14% of the Japanese population today. As NASH is the most progressive form of this disease, it has become a very important health issue to let doctors know how to recognize patients with NAFLD. In this paper, we discuss how to recognize NAFLD, including NASH, in our outpatient clinic.