A 35-year-old white woman was found to have persistently high platelet counts of >600 × 109/L for nearly 2 years. Her hemoglobin, mean corpuscular volume and white cell counts were normal. Blood film showed morphological abnormalities in red cells with plenty of acanthocytes, spiculated spherocytes, target cells, spherocytes, stomatocytes, and Howell-Jolly bodies. Platelet anisocytosis and giant platelets were also noted in the blood film (panels A and B). These blood film changes are commonly seen in hyposplenism, which can occur in the congenital absence of spleen, sickle cell disease, celiac disease, vasculitis, ulcerative colitis, essential thrombocythemia, and after splenectomy. This patient did not undergo splenectomy, but she had celiac disease and did not adhere to gluten-free dietary restrictions. Ultrasonography showed a normal-sized spleen, but a radionuclide liver-spleen scan revealed no splenic uptake. These findings were consistent with functional hyposplenism, which was deemed to be secondary to celiac disease. Bone marrow biopsy and JAK2-V617F and BCR-ABL mutation tests performed for evaluation of persistent thrombocytosis excluded a myeloproliferative neoplasm, thus confirming hyposplenism-associated thrombocytosis. The exact mechanism of hyposplenism in celiac disease is unclear. Life-threatening bacterial infections with pneumococci, meningococci, Haemophilus, and Capnocytophaga canimorsus can occur in patients with hyposplenism. The patient was counseled about hyposplenism, and pneumococcal, meningococcal, and Haemophilus influenzae type b vaccinations were administered.