Human metapneumovirus (hMPV) infections commonly present as mild upper respiratory tract infections in healthy adults, although severe respiratory complications have been observed, particularly in elderly and immunocompromised patients. We report a case in whom pneumonia caused by hMPV progressed to acute respiratory distress syndrome (ARDS) in a healthy adult without underlying diseases. A 31-year-old female presented with fever and dyspnea, prompting transfer to our hospital for mechanical ventilation 3 days after symptom onset. Auscultation revealed coarse breath sounds and crackles in both lung fields, and chest X-ray showed non-specific infiltrative nodules with poorly defined borders throughout both lungs. ARDS caused by community-acquired pneumonia was diagnosed. hMPV was identified via rapid testing of respiratory samples for genes that encode pneumonia pathogens and drug resistance markers; we employed reverse transcription polymerase chain reactions to these ends. Six days later, the patient was weaned off the mechanical ventilator, and discharged from the hospital in good clinical condition.