This is a 70 year old woman with a history of AHT and recently diagnosed with neoplasia of the lower rectum, treated with chemotherapy (5-fluorouracil analogue) and preoperative radiotherapy completed 2 months before surgery. She was admitted to the ICU after surgery (abdominoperineal amputation) due to suspected bronchoaspiration during anaesthetic induction with oximetric repercussions and ventilatory difficulties. She was sedoanalgesiated, intubated and connected to MV. Radiological findings showed no infiltrates indicative of parenchymal lung involvement. Initial evolution was good, and she was extubated without incident after 48h. She presented progressive worsening in the following 2 days radiologically (right basal parenchymal parenchymal involvement), gasometrically (non-invasive mechanical ventilation (NIV) was required to maintain pulse oximetry at over 90%) and clinically (persistent tachypnoea with poor respiratory mechanics), so she was reintubated. She started with a persistent fever of over 39oC, resistant to antipyretics and physical measures. Microbiological samples were taken (blood culture, urine culture and bronchoaspirate). Antibiotic treatment started in the operating theatre was maintained. Laboratory tests showed a significant inflammatory reaction with C-reactive protein of 50mg/dl without leukocyte reaction (<10,000×103/μl). She remained intubated and connected to MV for 7 days, during which time fever persisted with peaks over 39oC, with radiological improvement without infiltrates and persistently negative microbiological samples; an abdominal CT scan was performed and complications derived from the surgery were ruled out. The patient was extubated afebrile, with compensated blood gases and good response to spontaneous respiratory tests; despite optimal conditions at the time of extubation, she had to be reintubated in 12 hours due to respiratory failure. She again began with high fever and repeated negative cultures, so fibrobronchoscopy was performed with bronchoalveolar lavage (BAL) and samples were sent to microbiology (culture and PCR for herpes, CMV and respiratory viruses) and pathological anatomy. Percutaneous tracheostomy was performed and the BAL results were received, showing early positive HSV-1 PCR (qualitative test) and, histologically, the presence of cells showing multinucleated nuclei, with ground-glass chromatin and intranuclear inclusions; immunocytochemically, nuclear positivity for herpes virus was found. Antiviral treatment was started with acyclovir 10mg/kg/8h i.v. with clinical improvement, disappearance of fever and progressive disconnection of the respirator until full respiratory autonomy.