Objective: To determine the frequency and characteristics of dengue fever (DF) in patients of acute febrile illness presenting at a secondary care hospital. Methodology: The observational cross sectional study was carried out from May to October 2010 in Remedial Centre Karachi and included patients above the age of 12 years who presented with acute febrile illness. The WHO classification and case definitions were used to classify the disease as Dengue Fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Clinical, hematological and biochemical findings were recorded serially until discharge. Results: During the study period, 90 (34.75%) presented with typical features of DF, 28 (31.11%) were dengue proven, seven (7.7%) proved to be of malaria in which malarial parasites were found positive in the peripheral blood, while the remaining 55 (61.11%) patients were dengue probable. Age of the patients ranged from 13 to 76 years. Fever was the most common clinical presentation (100%) followed by vomiting 50 (55.56%), body ache 31 (34.44%) abdominal pain 17 (18.89%) and headache 9 (10%). Maculopapular rash was seen in 4(4.44%) patients. Laboratory findings included thrombocytopenia, leucopenia and raised alanine aminotransferase levels. Eighty one patients (90%) improved clinically and hematologically and were discharged in stable condition. Conclusion: Fever and thrombocytopenia were the most common presentation of dengue fever (DF). The overall mortality of DF is low, if treated appropriately. Awareness of health care professionals and public regarding preventive strategies is essential to fight against this disease.