"Pure" alcoholic fatty liver has been widely assumed to be "benign" with very low risk of progression to cirrhosis. Studies thus far have included either patients with coexisting recognised precursor lesions of cirrhosis or have been restricted to short-term histological follow-up. We have followed 88 patients, first seen between 1978 and 1985, with a histological diagnosis of pure alcoholic fatty liver and no evidence of fibrosis or alcoholic hepatitis, for a median of 10.5 years, to determine any factors predictive of disease progression. Of the 88, at follow-up nine had developed cirrhosis and a further seven fibrosis. Eight of nine patients with cirrhosis had continuing alcohol consumption of more than 40 units per week at follow-up; in the other patients, consumption was unknown. Independent histological predictors of progression on index biopsy were: presence of mixed macro/microvesicular fat, and presence of giant mitochondria. We can no longer regard alcoholic fatty liver as benign. In the presence of continuing high alcohol consumption the above histological features identified those at high risk (47-61%) of disease progression. Therefore, patients with these features should be counselled intensively regarding their alcohol consumption.