High prevalences of idiopathic hepatic lesions were found in mummichog, Fundulus heteroclitus from a site in the southern branch of the Elizabeth River, Virginia contaminated with polycyclic aromatic hydrocarbons (PAHs). Gross hepatic lesions occurred in 93% of the individuals from this site, whereas no hepatic lesions were detected in fish from two less contaminated sites. Lesions included foci of cellular alteration, hepatocellular adenoma, early and advanced hepatocellular carcinomas and cholangiocellular proliferative lesions. Advanced carcinomas exhibited several distinct cellular patterns and some livers contained multiple neoplasms occupying up to 80% of the hepatic parenchyma. These findings indicate a strong positive association between exposure to creosote-contaminated sediments and the high prevalence of hepatic neoplasms in a feral population of mummichog, and support the putative role of PAHs in fish hepatocarcinogenesis. Additionally, they suggest that the mummichog may be a useful indicator of exposure to carcinogens in aquatic environments.