Background: Dengue virus (DENV) is an arthropod borne flavivirus responsible of a major viral re-emergent disease in tropical and sub-tropical countries, affecting about 50 million people at year around the world. In Colombia dengue outbreaks occurs every five or six year, but the infection is endemic and constantly reported in most of the country. During the last year, Colombia went through the largest dengue epidemic occurred in decades, with 157.152 cases notified, 217 deaths confirmed and all four viral serotypes co-circulating. Methods: Samples from two fatal cases (serum from one patient and tissue from the other one) were tested by RT-PCR using separate dengue type specific primers. Results: Gel electrophoresis demonstrated amplification with two different serotypes (DENV2/DENV3 and DENV2/DENV4 respectively). Results were confirmed by sequence of the amplified fragments and further analysis in the Basic Local Alignement Search Tool (BLAST). Conclusion: Although the co-circulation of all 4 dengue serotypes is common in highly endemic areas, concurrent infection with 2 different serotypes remains as a very unusual event. This is the first report of dengue co-infection in fatal cases in Colombia. Nevertheless, the role of concurrent infection in severity of the disease should be further established.