Indroduction: Leptospirosis is a frequent cause of febrile illness around the world, particularly in tropical and subtropical areas such as Perú. Objective: To estimate the frequency and socio-demographic characteristics associated with leptospirosis in febrile patients in northern Perú. Materials and Methods: A cross sectional study was conducted from January to December 2014 in 143 fever cases admitted to the Hospital Regional Lambayeque, Perú. Structured for socio-demographic information and sanitation questionnaire was used. Serum samples were examined to quantitatively determine the presence of IgM antibodies to leptospira using ELISA IgM. Results: The frequency was 26.6% (95% CI 19.3 to 33.8) and independently associated features were: be between 20-54 years (OR: 3.36, 95% CI 1.17 to 9, 64), work in agriculture-livestock (OR: 6.15, 95% CI 1.99 to 19.05),contact with animals (OR: 4,13, IC 95%: 1,76-9,65) and consumption of unsafe water(OR: 3,33, IC 95%: 1,49-7,43). Conclusions: This study reveals a high frequency of leptospirosis among febrile patients from northern Perú. These results indicate the need to investigate routinely leptospirosis in febrile patients, especially those exhibiting risk characteristics.