This study has been done to differentiate clinical and biological parameter of co-infections from infections alone and to find out whether patients infected by both malaria and dengue were more severe than either infection alone. Material and Methods: All febrile adult patients (> 18 years of age) were investigated for malaria, dengue and other causes of fever. Patients of concurrent dengue and malaria (Group A) were compared with malaria mono-infection (Group B) and dengue mono-infection

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... C). Frequencies of alterations in clinical , biochemical, haematological parameters and outcome were determined in various groups. Data was analysed using appropriate statistical tests. Results: Out of these 340 patients, there were 52 (15.29%), 132 (38.82%), and 156 (45.88%) patients in Groups A, B, and C respectively. Prevalence of co-infection in our study was 25%. Features like prolonged fever (7.18+/-3.91), severe anemia (23.07%) and respiratory distress (7.69%) were comparable to malaria mono-infection whereas features like bleeding manifestations(15.38%), frontal or retro-orbital headache (80%), arthralgia (15.38%) and / elevated haematocrit were more like dengue mono-infection. Conclusion: In endemic areas for dengue and malaria, prolonged fever, severe anemia and respiratory distress (in dengue patients) and bleeding manifestations, frontal or retro-orbital headache, arthralgia and / elevated haematocrit level (in malaria patients) should raise the suspicion of co-infection and since a high prevalence of co-infection was found in our geographical area. We recommend that all the patients suspected for dual infections should be treated concomitantly for dengue and malaria in malaria endemic areas.