Objective: Leptomeningeal metastasis (LM) is a neurooncological complication of advanced cancer that has a poor prognosis. The incidence of LM is increasing due to advances in neuroimaging. At the same time, the development of new systemic treatments with poor central nervous system penetration has improved outcomes and survival. However, diagnosis of LM remains quite difficult due to clinical polymorphism, inconsistent imaging abnormalities, and the inconsistent presence of neoplastic cells in cerebrospinal fluid. Psychiatric manifestations can blur the neurological frame and confound management of this complication. Method: To illustrate these difficulties, we report the case of a patient with no past psychiatric history who presented with a manic episode that was attributed to a recurrence of leptomeningeal metastasis. Results: With this case report, we highlight the importance of referring the patient to a psychiatrist or a member of the psychooncology unit when new behavioral disorders present. Significance of results: Leptomeningeal metastases can elicit psychiatric consequences. A hypothesis of this diagnosis should be considered for cancer patients who present with sudden or recent profound mental changes during the course of their disease. Oncologists and neurooncologists should be aware of this possibility. Collaboration with a psychooncologist is recommended to better manage this neuropsychiatric pathology.