We report the case of an adolescent girl who presents with the 18q-syndrome, primary hypothyroidism, pernicious anemia and IgM hypogammaglobulinemia. Her karyotype was performed during infancy because of malformations and showed deletion of the long arm of chromosome 18. The patient had been treated with levothyroxine (Elthyrone) since age 13 when primary hypothyroidism was documented. A close hematological follow-up was then undertaken due to the presence of anti-parietal cell antibodies. A megaloblastic anemia of sudden offset led to the diagnosis of pernicious anemia by age 16, which was confirmed by a positive Shilling's test. Recently, the patient was found to have antimicrosome antibodies and moderate IgM hypogammaglobulinemia.