Cyclosporine A is a potent immunosuppressant used to prevent organ transplant rejection and treat various autoimmune diseases. However, cyclosporine A can also induce gingival overgrowth, which is characterized by increased extracellular matrix due to an altered balance between collagen synthesis and degradation. This study proposed to verify whether trans-glutaminase 2, an enzyme thought to be responsible for the assembly and remodelling of extracellular matrix, plays any role in the pathogenesis of cyclosporine A-induced gingival overgrowth. Cyclosporine A-induced gingival overgrowths were collected from 21 liver transplant patients and case-controlled with 20 non-hyperplastic gingival biopsies from healthy patients who had previous periodontal treatment. In both groups, the presence and tissue distribution of transglutaminase 2 were determined by immunohistochemistry and analyzed in comparison with the tissue morphology and expression of lymphocyte-related antigens (CD3 and CD20) and a vessel-related marker (CD34). Transglutaminase 2 expression showed a significant increase (2.6-fold) in the stromal component of cyclosporine A-treated patients compared with controls (p<0.001), which suggested that transglutaminase 2 had a role in the pathogenesis of the disease. Further studies should investigate the therapeutic effect of anti-transglutaminase 2 drugs (putrescine or 1,4-diamino-butane) in these patients.