We evaluated spleens (n = 26), appendices (n = 10) and branchial cleft cysts (n = 6) for TdT-positive cells in pediatric patients. In spleen, appendix and branchial cleft cysts the range of TdT-positivity was 0-13, 0-96 and 0-6 TdT+ cells/hpf, respectively. In spleens, scattered TdT+ cells were seen most frequently in periarteriolar lymphoid sheath regions.