Histiocytosis X, a term comprising three well-known disease complexes, may have dental mobility as a prodromal or major symptom. In each of three patients described, an oral finding predated the other symptoms. The earliest symptom in one patient was loosened teeth; in another, periodontosis-like symptoms were documented ten years before the patient's report of pelvic pain which led to a diagnosis of eosinophilic granuloma; in the third patient, premature eruption of the primary teeth the gingival bleeding was the prodromal symptom. The clinician should understand the significance of each finding and investigate them until a confirmatory diagnosis is made.