We report three patients with primary autoimmune thrombocytopenic purpura (ATP) who developed an absolute lymphocytosis (lymphocyte count > 5 x 10(9)/l) after splenectomy and with a lymphocyte count between 5.4 and 8.9 x 10(9)/l. An immunophenotype study showed that the peripheral blood lymphocytosis was a persistent NK cell expansion (CD2+, CD56+, CD3-), and was characterized by a typical large granular lymphocytes (LGL) morphology. Two of these three ATP patients were refractory to splenectomy.