Atypical chronic myeloid leukemia (aCML) is a rare chronic myeloproliferative disorder characterized by leukocytosis, absence of Philadelphia chromosome or BCR-ABL rearrangement, and marked myeloid dysplasia. The diagnosis of aCML is difficult and challenging, more so if the initial presentation is with blast crisis. In the absence of characteristic mutational profile, blast crisis of aCML can lead to significant diagnostic dilemma. We describe a case of refractory acute lymphoblastic leukemia (ALL), needing critical evaluation of hemopathological and cytogenetic abnormalities. It was hypothesized that patient had undiagnosed aCML and presented with lymphoid blast crisis. To our knowledge, this is the first described case of aCML presenting with lymphoid blast crisis.