Primary CNS lymphoma (PCNSL) accounts for 1-5% of all primary brain tumors. Early and accurate diagnosis of PCNSL is crucial for proper management and is more likely if a tumor is observed on imaging. We present the PCNSL case of 77-year-old man who developed abrupt neuropsychiatric features from 5 days ago. This case suggests that clinicians should be alert on the possibility of PCNSL and apply prompt MRI evaluation, when elderly patient with chronic heavy alcohol drinking history present abrupt complex neuropsychiatric symptoms in outpatient clinic.