Leptospirosis is an infection caused by . Leptospirosis causes disease in humans mainly in developing countries and also in countries with poor housing and sanitation, due to animals (mainly rats) that are potential sources of contamination. The clinical manifestations and the severity of leptospirosis are highly variable. We present the case of a 56-year-old female that was admitted to the emergency department with a three-week history of fever (38.4ºC), headache, dyspnea, and cough. There was a worsening of the patient's clinical status with respiratory failure and the necessity of admission to the intensive care unit for respiratory support with mechanical ventilation. The treatment was initiated with piperacillin and tazobactam, azithromycin, and steroids. There was a favorable evolution, and the patient was transferred to the internal medicine ward after 12 days with a suspected diagnosis of small vessel vasculitis and pneumonia. In the medical ward, after a careful anamnesis, leptospirosis was suspected and confirmed. The aim of this case report is to highlight the importance of a good anamnesis and the fact that an elaborate clinical history helps to consider new diagnostic hypotheses. Also intends to alert to the existence of leptospirosis in developed countries, a disease underdiagnosed in these countries.