A 4-year-old girl, asymptomatic and in good general health, is referred to a paediatric Haemato-Oncology centre for splenomegaly associated with mild anaemia and thrombocytopenia. Initial suspicion of leukaemia is ruled out after thorough clinical, laboratory and imaging evaluations. Negative infectious and haematological tests redirect the diagnostic path toward a rare disease. Beta-glucocerebrosidase assay reveals an enzymatic deficiency, confirmed by genetic testing showing two missense mutations consistent with Gaucher disease. This case highlights the importance of considering metabolic disorders in the differential diagnosis of splenomegaly.