Epidemiological studies have demonstrated that there is a correlation between oral lichen planus and chronic hepatitis C virus (HCV) infection. HCV RNA has been recently detected in epithelial cells from oral lichen planus lesions by reverse-transcription polymerase chain reaction (RT-PCR). However, this technique does not discriminate which types of cells are infected by the virus or if the viralThe hepatitis C virus (HCV) is the etiological agent of most cases of posttransfusional hepatitis. 1 The viral genome consists of a 9.4-kb-long single-stranded RNA molecule of positive polarity. 2 HCV is thought to replicate in the liver through an RNA intermediate of negative polarity. 3 HCV causes acute and chronic hepatitis in humans. 4 Chronic HCV infection is characterized by a wide spectrum of liver damage ranging from mild chronic hepatitis to cirrhosis, and even hepatocellular carcinoma. 5 On the other hand, several dermatological diseases such as cutaneous necrotizing vasculitis, mixed cryoglobulinemia, porphiria cutanea tarda, and lichen planus have been associated with HCV infection. 6 Lichen planus is a mucocutaneous disease characterized by a band-inflammatory infiltrate enriched in CD4-positive cells, vacuolating degeneration of the basal epithelial layer, and the presence of acidophilic bodies that may represent apoptotic keratinocytes. 7 Its etiology is unknown and may be caused by a cell-mediated immunological response to induced antigenic changes in the skin and mucosa epithelium. 8 The association between HCV infection and lichen planus comes from epidemiological studies that have shown that the prevalence of antibodies against HCV antigens (anti-HCV) is higher in patients with lichen planus than in the general population. [9][10][11] Recently, the presence of positive and negative HCV-RNA strands (which is evidence of viral replication) has been demonstrated by reverse-transcription polymerase chain reaction (RT-PCR) in mucosa biopsies from anti-HCV-positive patients with oral lichen planus. 12 However, because of the high sensitivity of the RT-PCR technique, these PCR products may come from blood that contaminates the biopsies. Furthermore, the presence of HCV RNA in epithelial oral cells has not been demonstrated by in situ hybridization. To establish a role for HCV in the pathology of lichen planus, morphological evidence of HCV replication in the cells of the lesion is needed.For this reason, in this report, we have analyzed the presence of positive and negative HCV-RNA strands by in situ hybridization in paraffin-embedded mucosa biopsies from patients diagnosed as having oral lichen planus and from patients with a chronic HCV infection, but without evidence of suffering oral lichen planus. PATIENTS AND METHODSPatients. Paraffin-embedded oral mucosa biopsies from 23 patients clinically diagnosed as having oral lichen planus were analyzed in this study. Oral mucosa biopsies from the jugal mucosa were obtained to confirm the clinical diagnosis. After the histological examination, the remaining tiss...