INTRODUCTION: Gingival overgrowth associated with immunosuppression following liver transplantation is a commonly recognized clinical problem. The aims of this study were to determine the incidence of gingival overgrowth in a group of children post liver transplantation and to compare gingival overgrowth in children receiving FK506 with those receiving cyclosporin. METHODS: Seventy-nine children (aged 15-196 months) undergoing liver transplantation at Birmingham Children's Hospital between October 1998 and October 2000 were studied. Gingival overgrowth was assessed in a blinded fashion and scored in a previously validated manner. Gingival overgrowth scores of the patients on each immunosuppressant drug were then compared. RESULTS: Fifty-two patients were treated with cyclosporin and 27 treated with tacrolimus. Eighteen children were also receiving nifedipine (also known to cause gingival overgrowth) and were considered separately. Of the 41 children receiving cyclosporin alone, 26 exhibited gingival overgrowth compared to zero of 20 patients receiving tacrolimus alone. Those children treated with immunosuppression plus nifedipine developed gingival overgrowth, however, this was much less marked in the tacrolimus group. CONCLUSION: Tacrolimus, unlike cyclosporin, is not associated with gingival overgrowth when used for immunosuppression following liver transplantation in children, and may be the drug of choice for children.