A case of 54 year-old male with a past medical history of metastatic rectal adenocarcinoma. He presented with progressively worsening left leg pain for several months. The initial investigations revealed signs of systemic inflammatory response syndrome (heart rate 113/min, leucocytes 34.19 x 10³/ul) and elevated inflammatory parameter (procalcitonin 15.16 ng/ml). Even with the empirical piperacillin-tazobactam and vancomycin treatment, he rapidly progressed to severe sepsis. After 8 hours of admission, his mental status declined. Without a history of recent head trauma, cranial computed tomography showed minimal pneumocephalus in the lateral ventricles and cisterns. Because of hemodynamic instability, lumbar puncture and cranial magnetic resonance imaging could not be performed. Despite appropriate treatment for septic shock with fluid resuscitation, vasopressors and antibiotics, he developed cardiac arrest. Unfortunately, cardiopulmonary resuscitation was unsuccessful. He died 14 hours after admission. Two samples of blood culture confirmed Clostridium septicum septicemia which raised the diagnosis of meningoencephalitis and pneumocephalus caused by this organism.