A 58-year-old Japanese male visited us with painful lesions on the lower lip, oral mucosa and genital region of an 8-month duration. Histological features of the genital lesion were almost consistent with lichenoid tissue reaction. A few intraepidermal acantholytic keratinocytes were also seen in the suprabasal clefts. Direct immunofluorescence exhibited cell surface immunoglobulin (Ig)G deposition and linear deposition of fibrinogen at the dermoepidermal junction. IgG anti-desmoglein (Dsg)3 antibody, but not anti-Dsg1 antibody, was detected in the patient's serum by enzyme-linked immunosorbent assay. Immunoblotting using normal human epidermal extract detected the 210-kD envoplakin, 190-kD periplakin and 130-kD Dsg3. The diagnosis of paraneoplastic pemphigus (PNP) was made. Subsequent investigation revealed a large space-occupying lesion in the liver. Histological findings from liver biopsy specimen were consistent with hepatocellular carcinoma. The patient has been alive 38 months after the diagnosis of PNP was made, although the liver mass has slowly enlarged. Our case is clinically and histologically similar to erosive mucosal lichen planus. Immunological studies confirmed the diagnosis of PNP. The results of negative Dsg1 and positive Dsg3 were consistent with clinical features showing severe mucosal involvement without cutaneous erosion. In PNP, the association with non-hematological solid tumor is extremely rare.