Background and aims: Fatty liver is a common histological finding in human liver biopsy specimens. It affects 10–24% of the general population and is believed to be a marker of risk of later chronic liver disease. The present study examined the risk of development of cirrhotic liver disease and the risk of death in a cohort diagnosed with pure fatty liver without inflammation. Methods: A total of 215 patients who had a liver biopsy performed during the period 1976–1987 were included in the study. The population consisted of 109 non-alcoholic and 106 alcoholic fatty liver patients. Median follow up time was 16.7 (0.2–21.9) years in the non-alcoholic and 9.2 (0.6–23.1) years in the alcoholic group. Systematic data collection was carried out by review of all medical records. All members of the study cohort were linked through their unique personal identification number to the National Registry of Patients and the nationwide Registry of Causes of Death, and all admissions, discharge diagnoses, and causes of death were obtained. Results: In the non-alcoholic fatty liver group, one patient developed cirrhosis during the follow up period compared with 22 patients in the alcoholic group. Survival estimates were significantly (p<0.01) different between the two groups, for men as well as for women, with a higher death rate in the alcoholic fatty liver group. Survival estimates in the non-alcoholic fatty liver group were not different from the Danish population. Conclusions: This study revealed that patients with type 1 non-alcoholic fatty liver disease have a benign clinical course without excess mortality.