This is a case of a 56-year-old man with Castleman disease (CD) who improved after kidney transplantation (KTP). CD is an uncommon lymphoproliferative disorder that was found incidentally on biopsy during dialysis in the current patient and was followed up without further treatment. However, the lesion showed improvement after KTP. Therefore, active KTP can be considered even if CD is one of the lymphoproliferative disorders that can occur as a complication after KTP.