Mucormycosis is a rare invasive fungal disease in pediatric patients with hematological malignancies and is associated with poor outcomes. We present a fulminant and ultimately fatal case of rhino-orbito-cerebral mucormycosis, addressing important issues including clinical signs and symptoms, diagnostic approaches and the challenges of timely diagnosis. The patient was an 11-year old girl undergoing re-induction chemotherapy for Central Nervous System relapse of B-cell precursor acute lymphoblastic leukemia. She presented six days into the second course of chemotherapy in profound neutropenia with aggravating headaches, painful abducens nerve palsy and anisocoria. At first (day -3), no significant radiological or ophthalmological correlations were found, and methyl-prednisolone was started due to suspected vasculitis following ICU admission. After further clinical deterioration, a second MRI scan (day 0) revealed a prolonged occlusion of the left carotid artery, which was successfully stented in a neuroradiological intervention (day +1). However, during the next day the child developed clinical signs indicating severe cerebral dysfunction. An emergency CT scan showed complete infarction of the left hemisphere including a progredient perfusion deficit and beginning brain edema. Based on the unfavorable prognosis, best supportive care was initiated, and the patient deceased on day +2. Pathological and microbiological workup identified thrombotic infarction in all major cerebral arteries. While microscopy was suspicious for mucormycosis, nested PCR from retained blood specimens confirmed the genus Lichtheimia. Final NGS on brain tissue led to the identification of Lichtheimia ramosa. This case illustrates the rapidity and severity of Mucorales infection. It shows the importance of early clinical suspicion and the need for an aggressive laboratory testing algorithms. The stratification of risk factors and definition of red flags may be a future task fighting these infections.