We describe a case of a 36-year-old woman with no psychiatric or somatic history who was presented to the emergency department with a profound change in mental status, more precisely a catatonic status and auditory hallucinations. Due to the unclear aetiology and suspicion of underlying psychiatric problems, the patient was admitted to the psychiatric ward. After discharge against medical advice, readmission was necessary due to deterioration and sudden onset of myoclonus. On further examination, acute disseminated encephalomyelitis (ADEM) was diagnosed. This case illustrates that ADEM can present itself as an initial psychiatric problem and emphasizes the importance of extensive medical clearance at presentation and continued attention for possible somatic origin, even when the initial clearance turns out to be negative.