A retrospective chart review of 500 leukemia patients was carried out to analyze the role of oral pathoses in the presentation of leukemia and to determine those factors which affect the frequency of oral involvement during the initial clinical phases of the disease. The data indicate that oral pathoses were frequent signs or symptoms in patients with undiagnosed acute leukemia but were less prevalent in patients with undiagnosed chronic leukemia. Neither age nor sex appeared to be a significant factor affecting oral involvement. Oral signs of thrombocytopenia were the most prevalent complaint of patients seeking diagnosis for their leukemia because of an oral problem, and they were also most frequently responsible for oral problems found at initial physical examination. Head and neck lymphadenopathy was also a frequent presenting sign or symptom. Dentists were responsible for initiating the diagnosis of leukemia in a significant number of patients with acute nonlymphoblastic leukemia.