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Pulmonary alveolar proteinosis (PAP) is a rare condition characterised by impaired alveolar macrophage-mediated surfactant clearance, resulting in the accumulation of lipoproteinaceous material within the alveoli. Secondary PAP has been associated with certain medications. Ruxolitinib, a Janus kinase 1/2 inhibitor has recently been implicated in rare cases of PAP.We report the case of a woman in her early 60s treated with ruxolitinib for chronic pulmonary graft-versus-host disease following an allogeneic haematopoietic stem cell transplant for acute lymphoblastic leukaemia, who developed progressive exertional dyspnoea. High-resolution CT demonstrated a 'crazy paving' pattern, and bronchoalveolar lavage revealed periodic acid-Schiff positive granular material consistent with PAP. Microbiological studies were negative. Ruxolitinib was discontinued with subsequent symptomatic, radiological and lung function improvement.This case highlights ruxolitinib as a potential cause of secondary PAP and emphasises the importance of considering this rare complication in patients who develop new respiratory symptoms while receiving ruxolitinib.