Dengue is one of the significant public health concerns in endemic countries. With plasma leakage as the primary pathophysiology in the process of severe dengue infection with hemoconcentration and thrombocytopenia being the significant laboratory diagnostic features in children, the presentation in children with underlying hemato-oncological conditions is atypical and often, anemia is found in these children, instead of hemoconcentration. We describe a young boy with beta thalassemia major who underwent splenectomy for hypersplenism 5-months ago with dengue illness, characterized by features mimicking a severe post splenectomy opportunistic infection with fever, loose stools and abdomen tenderness. Leucopenia, thrombocytopenia, minimal pleural effusion, ascites and gall bladder wall edema prompted us to think of dengue and was found to be positive. Child improved with appropriate supportive care measures. Pediatricians should be aware of the differences in the presentation of tropical infections in children with hemato-oncological disorders. Tropical infections should be kept in mind even in children with underlying hemato-oncological conditions, to ensure diagnosis and appropriate management.