Acute lymphoblastic leukemia (ALL) is a rare cause of hypereosinophilia (HE). We present a case of B-ALL and HE-associated lung inflammation to shed light on the diagnostic challenges in this rare entity. Bone marrow examination in the context of persistent HE is crucial, even in the absence of other cellular morphological abnormalities in the peripheral blood. This form of ALL is associated with severe complications and inferior outcome due to HE-induced organ damage, therefore a quick initiation of therapy is essential. Furthermore, reports of higher incidence of thromboembolic complications merit careful monitoring during therapy and evaluation of prophylactic measures.