ABSTRACT Introduction: Listeriosis in immunocompetent patients usually presents as gastroenteritis with fever; however, it can occasionally lead to severe infections such as meningitis and sepsis. The case report concerns a boy with several autoimmune diseases on immunosuppressive therapy, who developed behavioural issues due to Listeria monocytogenes (LM) infection. Case Report: The patient was suspected of meningitis, and polymerase chain reaction testing of the cerebrospinal fluid revealed the presence of LM. The patient’s condition worsened, neurological symptoms increased, and the patient developed sepsis, requiring treatment in the Intensive Care Unit (ICU). After a monthly stay in the ICU, contact with the patient returned, but the infection caused severe behavioural changes. Autoimmune encephalitis was suspected and psychiatric treatment initiated. Conclusions: This case illustrates the broader issue of LM infection and emphasizes the need for special attention in the care of immunocompromised patients.