Precursor T-cell acute lymphoblastic leukaemia (T-ALL)/lymphoma (T-LBL) is a neoplasm with cytological features that include blast cells of medium size, high nuclear cytoplasmic ratio and inconspicuous nucleoli, which are usually TdT (Terminal Deoxynucleotidyl Transferase) positive and variably express T-cell markers. We report a case of T-ALL with atypical cytological presentation which showed lymphoblasts with homogenous nuclear pattern, larger amounts of cytoplasm with vacuoles and prominent nucleoli. A 56-year-old male was hospitalized due to high fever and kidney infection. Further examination confirmed anemia, thrombocytopenia, normal level of white blood cells and high level of lactat-dehydrogenase (LDH). Bone marrow aspiration revealed 87% and peripheral blood 41% of lymphoblasts with cytoplasmic vacuoles which suggested Burkitt lymphoma (BL) morphology. Patient's karyotype showed no chromosomal aberations. Identification of immunophenotype discovered cells which were CD2 and CD3 positive and CD20 negative with focal acid phosphatase activity in 67% of blasts. This excluded Burkitt lymphoma and led to diagnosis of T-ALL. The patient was submitted to two cycles of chemotherapy, autologous stem cell transplantation, and intrathecal chemotherapy, but he died after 10 months because of disease complications (lung aspergillosis and pleural effusion). Our case report showed how morphology alone can be misleading and sometimes is not enough in diagnosing ALL. Beside morphologic criteria, setting correct diagnosis depends on identification of immunophenotype by flow cytometry and cytogenetic-molecular abnormalities. Further improvements in the molecular definition of ALL subtypes, development of new and targeted drugs will improve patient's outcome and prognosis.