We describe a child with thrombocytopenia-absent radius (TAR) syndrome in whom a refractory Langerhans cell histiocytosis (LCH) developed at 9 years. Recently, it has been demonstrated, in a large cohort of patients with TAR syndrome, that microdeletion on chromosome 1q21.1 is the characteristic genetic alteration. This genetic alteration was found in the affected son and in maternal lineage. Our data confirm the role played by the 1q21.1 microdeletion in the pathogenesis of TAR syndrome proposing a panel of polymorphic markers for a rapid and low-cost screening of 1q21.1 microdeletion. We do not know if the occurrence of two rare diseases as of TAR syndrome and LCH could be considered a chance association; at our knowledge, a genetic link does not seem to be present between the diseases. Descriptions of additional cases of LCH in patients with TAR syndrome are necessary before a cause and effect relationship can be proven.