Introduction: Proteus syndrome (PS) is an exceptionally rare disorder characterized by asymmetrical overgrowth of the skin, bones, muscles, adipose and connective tissues as well as blood and lymphatic vessels. Case presentation: We describe the clinical case of a 6.5-year-old girl with PS diagnosed and treated at the Institute for Mother and Child Health Care of Serbia "Dr Vukan Čupić". When she was 11 months old, she was treated for pneumococcal sepsis and meningitis. The disease was complicated by intracranial thromboses of venous sinuses, subdural empyema, brain infarction and a severe neurological deficit in the acute phase. Additionally, portal and mesenteric venous thromboses were identified. At 2.5 years of age, echocardiography and cardiac magnetic resonance revealed an ascending aortic aneurysm. The patient suddenly passed away when she was 6.5 years old and the cause of death has remained unknown. Conclusion: Despite aggressive antibiotic therapy, our patient with PS experienced multiple life-threatening complications associated with pneumococcal disease. Considering the previously documented immune disturbances in PS patients, it is plausible to speculate that our patient's immune system was compromised due to the primary diagnosis. However, as data on the immunological response in PS patients are scarce, conclusive evidence regarding the predisposition to serious infections necessitates further comprehensive studies.