The present study has investigated the relationship between pancreatic lymphatics, infiltrating cells, and insulitic development after a single injection of complete Freund's adjuvant (CFA) given at an early age in the nonobese diabetic (NOD) mice. No CFA‐treated NOD mice developed hyperglycemia, whereas most CFA‐untreated mice died of diabetes at the age of 20–30 weeks. In untreated NOD mice, the increased infiltration of dendritic cells (DCs) and T‐lymphocytes into the pancreatic islets appeared to be consistent with the increased expression of the secondary lymphoid chemokine (CCL21) and CD₃₁ by the endothelial cell lining of inter‐ and intralobular lymphatics. As the infiltration became severe, the reaction products of CCL21 and CD₃₁ were distributed in the nucleus and cytoplasm of lymphatic endothelial cells (LECs), through which DCs and T‐lymphocytes migrated frequently. Administration of CFA reduced the number of infiltrating DCs and T‐lymphocytes, but did not affect macrophage infiltration. The peri‐insulitis occurred in numerous islets of CFA‐treated NOD mice without the appearance of the intraislet infiltration and islet‐associated lymphoid‐like tissues. Furthermore, significant suppression of CCL21 and CD₃₁ was demonstrated on the infiltrating cells to the islets and islet‐associated lymphatics. The abluminal endothelial cell lining of lymphatic vessels exhibited weaker immunoreactivity of CCL21 and CD₃₁ in comparison with the luminal surfaces. The reaction product of 5′‐nucleotidase (5′‐Nase) was evenly deposited on LECs, which were the absence of open junctions, cytoplasmic protrusions, and vesicles. CFA treatment influenced the migratory processes of the infiltrating cell, which were closely related with structural changes of pancreatic lymphatics and inhibited insulitic development. These findings suggest that in CFA‐treated NOD mice, the suppression of insulitis and prevention of diabetes are secondary to the functional modulation of pancreatic lymphatics and infiltrating cells. © 2004 Wiley‐Liss, Inc.