Objectives The aim of this study was to evaluate serum prolactin (PRL) as a potential tumor marker in the detection of hepatocellular carcinoma (HCC). Background HCC ranks fifth among the most prevalent cancers worldwide. In Egypt, the incidence of HCC had been doubling because of hepatitis C viral infection. New serum tumor markers are required for the diagnosis of HCC instead of α-fetoprotein (AFP) (the most widely used marker) due to its poor diagnostic accuracy. Prolactin receptor has been identified in a variety of human tissues, such as the liver. When PRL binds to its receptor, it leads to the activation of Janus kinase 2, a tyrosine kinase that can phosphorylate the STAT (signal transducer and activator of transcription) proteins and subsequently functions in cell proliferation and differentiation. Patients and methods Eighty adult patients were selected for this study. They were categorized as follows: group I, which included 10 healthy controls, age and sex matched; group II, which included 40 patients with cirrhosis; and group III, which included four patients with newly diagnosed HCC in addition to cirrhosis. Routine tests for liver cirrhosis and HCC were carried out. Serum PRL was measured using enzyme-linked immunosorbent assay. Results Serum PRL was significantly elevated in the HCC group when compared with the other two groups. There was a significant difference between single and multiple lesions as regards PRL level in the HCC group; it was higher in cases of multiple lesions. Significant positive correlations were found between PRL on one hand and AFP, aspartate aminotransferase platelet ratio index, and tumor size on the other hand. At a cutoff level of at least 44.5 ng/ml, serum PRL had 92.5% sensitivity, 77.5% specificity, 80.43% positive protective value, and 91.18% negative protective value for the diagnosis of HCC. Conclusion Significantly elevated serum PRL in HCC patients may act as promising and potentially complementary biomarker with AFP. It may offer more effective early detection of HCC.