OBJECTIVE: This study was carried out to determine the prevalence of leptospirosis among febrile patients with a suspicious clinical diagnosis of dengue fever in northern Peru. RESULTS: A total of 276 serum samples from patients with acute febrile illness (AFI) and suspected diagnosis for dengue virus (DENV) were analyzed. We identified an etiological agent in 121 (47.5%) patients, DENV was detected in 30.4% of the cases, leptospirosis in 11.2% and co-infection by both pathogens was observed in 5.9% of the patients. In this study the most common clinical symptoms reported by the patients were: headache 89.1%, myalgias 86.9% and arthralgias 82.9%. No differences in symptomatology was observed among the different study groups