Diffuse alveolar hemorrhage (DAH) sometimes causes a life-threatening condition; thus, prompt diagnosis and treatment for DAH is crucial. However, a variety of diseases (e.g., systemic autoimmune diseases, infectious diseases, drugs) are associated with the development of DAH, which occasionally causes diffi culty with identifying the specifi c etiology. [1] Synthetic cathinones (SCs) have gained popularity as a recreational drug since 2012 in Japan, and SC intoxication sometimes results in organ dysfunction. [2,3] However cases of DAH following SC intoxication have not previously been reported. [2][3][4][5][6] We here present a 28-year-old man in hypoxic respiratory failure due to DAH. Although tests failed to identify the underlying cause of DAH, he recovered spontaneously and was discharged without any complications. About 2 months later, he was brought to our hospital again with mild DAH. According to the pharmacological aspect of SCs, which he confessed to inhale, we finally elucidated that the cause for DAH could be SC intoxication.