Langerhans-cell histiocytosis (LCH) is caused by an uncontrolled pathogenic clonal proliferation of dendritic cells (DCs) with Langerhans-cell (LC) characteristics. LCH cells are arrested in an immature, partially activated stage and show a deviant regulation of cell division. Their aberrant interactions with T cells and the lesional microenvironment are typified by high level production of diverse cytokines. Chemokine and chemokine receptor patterns probably explain LCH predilection sites and lesion composition, reminiscent of chronic granulomatous inflammation. Recent advances in LCH immunology suggest that clonal changes in DCs might underlie the aberrant immune interaction with T cells, leading to a unique pathological picture, which combines features of carcinogenesis and chronic inflammation.