Resumen Objetivos: Describir el comportamiento epidemiologico de la leptospirosis en el departamento del Atlantico (Colombia), de enero de 1999 a marzo del 2004. Metodologia: Estudio descriptivo. Se analizaron 970 muestras unicas de pacientes sospechosos de infecciones con Leptospira en el Laboratorio Departamental del Atlantico mediante Aglutinacion Microscopica (MAT), usando como antigenos los serovares Icterohemorragiae, Pomona, Canicola, Hardjo, Grippotyphosa y Hardjo-bovis de Leptospira interrogans. Informacion adicional sobre la clinica de pacientes a traves de fichas epidemiologicas y visitas a hospitales, ademas de datos de precipitacion anual, fue obtenida. Resultados: El 9,7% de los casos fueron positivos para Leptospira, siendo los serovares Icterohaemor- rhagiae (62%) y Hardjo (12,8%) los mas frecuentes. La mayoria de casos (61%), se presentaron en hombres entre 15 y 45 anos de edad y la clinica mas comun se asocio a fiebre (91,7%), mialgias (72,2%), vomito/nausea (70,8%), cefalea (68,1%) e ictericia (63,9%). El 8.6% de los casos asociados a infec- ciones con el serovar Ictherohemorragiae fueron severos; la sintomatologia coincidio con el sindrome de Weil, pero no se registraron fatalidades. En los anos 2003(23), 2001(21) y 2002(18) se registro la mayor incidencia de casos, en meses de alta precipitacion (Agosto-Noviembre). Los municipios con mayor numero de casos fueron Barranquilla (46), Soledad (25), Puerto Colombia (6) y Galapa (6). Conclusiones: La leptospirosis debe tenerse en cuenta dentro del diagnostico diferencial de otras entidades comunes en la region (fiebre de dengue). Un diligenciamiento completo de la ficha epidemio- logica permitira un estudio mas detallado de esta patologia, para desarrollar programas de vigilancia y prevencion eficaces. Palabras claves: Leptospira, serologia, Atlantico, Colombia. Abstract Objective: This study was performed to describe the epidemiological situation of Leptospira in the Departament of Atlantico (Colombia), from January 1999 to March 2004. Methods: A descriptive study was performed. A total of 970 single serum samples from patients with suspected Leptospira infections, were analyzed using the microscopic agglutination test (MAT). The serovars of Icterohaemorrhagiae, Pomona, Canicola, Hardjo, Grippotyphosa and Hardjo-bovis belonging to L. interrogans, were used as antigens. Information about clinical presentation based on epidemiological sheets, visits to patients and climatological data were obtained. Results: The 9,7% samples were IgM positive for Leptospira and the most prevalent was the serovar Icterohaemorrhagiae (62%), followed by Hardjo (12.8%). Most of the patients were male (61%) between 15 and 45 y.o. The most common presenting features in these patients were (91.7%), myalgia (72%), vomit/nausea (70.8%), headache (68.1%) and icterichia (63.9%). 8.6% of the cases were severe, associated to infections with the serovar Icterohemorragiae and their symptomathology was similar to the Weil s syndrome; no fatalities were registered. The highest incidences were recorded during the years 2003 (23), 2001(21) and 2002 (18) especially during the rainy season (August-November). Barranquilla reported the highest number of cases (46) followed by Soledad (25), Puerto Colombia (6) and Galapa (6). Conclusions: Since leptospirosis is an increasing public health problem in the Caribbean Region, dif- ferential diagnosis with other similar pathologies (dengue fever, dengue haemorrhagic fever) has to be performed and surveillance and preventive programmes must be implemented. Key words: Leptospirosis, serology, Atlantico, Colombia.