ObjectiveTo investigate the occurrence of MDR1 C3435T gene polymorphisms in the Turkish renal transplant patients treated with cyclosporine (CsA), and correlate these findings with prevalence and degree of gingival hyperplasia (GH). MethodsBefore to renal transplantation, dental treatment and oral hygiene education of 300 renal disease patients was completed. Peripheral blood samples were collected from 154 renal transplant recipients on CsA treatment without calcium channel blockers. MDR1 C3435T gene polymorphism and GH were analyzed at posttransplant month 6. ResultsNo difference was detected among groups for age, posttransplant period, creatine levels, serum concentration of CsA, or plaque and bleeding indices (P > .05). Out of all transplanted patients, 42.8% were found to have the heterozygote genotype. This was reduced to 37.5% when individuals with GH were taken into account. However, when degree of GH was analyzed, those with severe GH were found to have the heterozygote genotype significantly more often (P < .05). ConclusionsThe MDR1 gene polymorphism is not associated with GH frequency, but may be associated with GH severity.