Zygomycosis is an emerging fungal infection that is associated with high mortality in hematological patients and stem cell transplantation (SCT) recipients. Radiology--computed tomography (CT) imaging in particular--facilitates the detection of lung involvement at an early stage of the infection. The reversed halo sign (RHS) has previously been reported in cryptogenetic organizing pneumonia and, more recently, as a manifestation of pulmonary zygomycosis. Here we describe a case of histologically proven zygomycosis due to Rhizopus microsporus in a SCT recipient. A chest CT scan performed on day +6 due to persistent fever unresponsive to antibiotics revealed the presence of the RHS, i.e., a focal ground-glass opacity mass surrounded by a solid ring of consolidation. The patient was treated with a combination of liposomal amphotericin B, caspofungin, and deferasirox, but subsequently developed a large pneumothorax and died on day +49 due to progressive infection. This case supports earlier observations that RHS may be an early radiological sign of zygomycosis, facilitating an aggressive diagnostic strategy.