The purpose of this research was to study the occurrence of gingival overgrowth (GO) in children after kidney transplantation and to investigate the relationship of GO to medical and dental parameters. Forty-nine kidney transplant patients taking the immunosuppressive drug cyclosporine A (CsA) were evaluated for plaque (PI), calculus (CI), gingival inflammation (GI), probing depth (PD), width of keratinized gingiva (GW), and gingival overgrowth (GO). Blood trough levels and oral dosages of CsA were obtained from medical charts on the day of examination. Most (77.5%) subjects exhibited GO, suggesting that GO is a frequent problem in children and adolescents ingesting CsA. GI, PD, and GW were found to be statistically significantly greater in subjects with GO than in those without GO. CsA dose/day was not significantly different between subjects with GO and those without GO. CsA dose/kg body weight and blood trough levels of CsA were significantly higher in subjects without GO, but the average length of time subjects without GO had been ingesting CsA was only 1.3 months, compared with an average 3.5 years for subjects with GO. The results indicate that in young subjects, duration of CsA ingestion may be the most critical factor related to eventual GO development.