Id-1 is a member of the helix-loop-helix protein family and is involved in multiple biological processes, including development, proliferation, angiogenesis and carcinogenesis. However, the role of Id-1 in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) is still unclear. In this study, Id-1 expression in 96 tumor specimens of HBV-related HCC was detected by immunohistochemical (IHC) staining. The relationship between the Id-1 expression grade and patient clinicopathological features was studied. In addition, the relationship between Id-1 expression and disease-free and overall survival times was analyzed. Colocalization of Id-1 and HBx was investigated by confocal laser scanning microscopy. The effect of HBx on Id-1 expression was studied in vitro using the HepG2 HCC cell line. Overexpression of Id-1 was found in 64.6% (62/96) of tumor specimens and was correlated with the histological grade, portal vein invasion, lymph node metastasis, HBsAg and Child-Pugh classification. Patients with Id-1 overexpression had both shorter disease-free and overall survival times. Besides, colocalization of Id-1 and HBx was found by paired IHC and confocal study. The expression of Id-1 was positively correlated to that of HBx. In vitro ectopic expression of HBx in HepG2 cells significantly increased Id-1 mRNA and protein expression. To our knowledge, this is the first report suggesting that Id-1 expression is at least partially regulated by HBx and may serve as a potential prognostic marker for HBV-related HCC.