Epidemics of Dengue fever (DF) and Dengue hemorrhagic fever (DHF) are common in Southeast Asia. DF is defined & classified according to WHO criteria. Variable clinical manifestations of DF & DHF have been described in earlier studies. But some patients present with unusual clinical features and clinical profile not classifiable according to the present WHO criteria. Some of these complications if not recognized early and treated properly can even prove fatal. So this study was done to describe various clinical features in Dengue fever with special emphasis on unusual manifestations. This study was conducted at University College of Medical Sciences and associated Guru Teg Bahadur hospital; a tertiary care hospital, located in East Delhi in India. It was a retrospective study of 76 patients of probable DF; including 4 cases of DHF (according to WHO classification); 60 males & 16 females above 12 years of age admitted in medical wards of Guru Teg Bahadur hospital in an outbreak of DF which occurred during September-December 2009. The data obtained was analyzed to see clinical and laboratory profile of DF/DHF with special emphasis on unusual manifestations. The mean age of the patients was 28 +/- 9.6 years. Fever was present in all the cases with an average duration of fever being 5.47 +/- 2.2 days with body ache, (84.2%), vomiting (61.8%), abdominal pain (51.3%) and headache (19.7%) being the other presenting complaints. Hemorrhagic manifestations in the form of gum bleeding and epistaxis (35.5%), positive tourniquet test (27.6%); skin rashes (15.8%), melena (15.8%) and hematemesis (5.26%) were also present. In our study a fair no of patients presented with unusual symptoms like pain in abdomen 39 (51.3%), nausea 32 (42.1%), & vomiting 47 (61.8%), which is higher than that reported previous outbreak. Of the 39 patients who presented with abdominal pain; ultrasonography of abdomen was done in 25 patients. Fifteen (38%) of these were found to have acalculous cholecystitis. Amongst the known manifestations of DF, abdominal pain has been well described, but acalculous cholecystitis as a cause of abdominal pain is scantly reported. Another unusual manifestation was the presentation of patients (7.89%) in circulatory failure without the evidence of plasma leakage and not fulfilling all the criterion proposed by WHO for DHF/DSS. All of the above patients had very low platelet counts & tourniquet test was positive in all these six patients. Hepatomegaly and splenomegaly were observed in 34.2% and 7.89% of cases, respectively. Renal dysfunction was observed in 13.1% of cases. Laboratory investigations revealed thrombocytopenia (with a platelet count of < 100,000/microl) in all cases. Leucopenia (WBC < 4,000/mm2) and Hemoconcentration (Hct > 20% of expected for age and sex) were found in 38% and 5.26% of the cases, respectively. Results of our study indicate that apart from usual manifestations, sometimes unusual but clinically extremely important manifestations can occur which if not detected early can prove fatal. So a vigilant and timely approach is warranted.