<p><strong>Objective</strong>. To describe a severe case of infection by <em>Leptospira </em>in a woman in the northwest of Mexico<em>.</em></p><p><strong>Case report</strong>. A 55-yearold woman from Sonora, Mexico arrived at the Intensive Care Unit due to severe multiple organ failure primarily affecting the respiratory, renal and hepatic systems. Diagnostic tests were performed, and they were positive for anti-<em>Leptospira </em>antibodies, IgM and IgG; and spirochetes were observed on dark field microscopy and confirmed by Polymerase Chain Reaction (PCR). Doxycycline and platelet apheresis transfusion were used as treatment, which led to a very slow recovery.</p><p><strong>Conclusion</strong>. The information presented in this study may help in the identification of pathology caused by spirochetes. This case report is the first to present a case of severe leptospirosis in Sonora, Mexico.</p>