The authors present the case of a 19-year old man presenting to the emergency department with a 2-day history of left eye pain and ptosis, facial pain around the maxillae, coryza, headaches and fevers. He had a background of autism, mild learning disability, obsessive-compulsive disorder and asthma. Within the last month, his risperidone and sertraline doses had been increased. Basic observations and investigations suggested sepsis: tachypnoea, sinus tachycardia, fever and a raised white cell count and C reactive protein level. A CT head showed sinonasal polyposis and moderate chronic rhinosinusitis, with normal intracranial appearances. An MRI head showed evidence of extension of frontal sinus infection through the posterior wall of the left frontal sinus with subsequent left frontal extradural empyema. Intravenous antibiotics and surgical drainage of the left frontal sinus resulted in clinical improvement and discharge to complete the course of antibiotics in the community.