We describe the cases of two patients with fever initially diagnosed as dengue and urinary tract infection. The patients were inmates of the same prison and were in contact with stagnant drinking water, which is considered to be the likely site of contamination, about 2 weeks before the onset of the symptoms during the carnival celebrations. The time between the hospital admission and suspected leptospirosis (and starting specific treatment) was four days for the patient in case 1 and two days for case 2; between admission and laboratory diagnostic confirmation was ten days for case 1 and four days for case 2. We conclude that Leptospirosis is not considered as an option in the initial differential diagnosis but only after ruling out other pathologies.