Background: Fever is a common manifestation of an illness. Thrombocytopenia is most frequent finding in febrile illness. Thrombocytopenia with fever narrows the differential diagnosis of clinical entity and helps in reaching the diagnosis of febrile illness. The present study is carried out to find the cause of thrombocytopenia with fever and to assess the clinical complication associated with severity of thrombocytopenia and fever. Material and Method: This study was carried out in the department of general medicine Mata Gujri Memorial Medical College in Kishanganj, Bihar during the period of July 2021 to September 2022. Total 100 patients were enrolled in this study. Informed written consent was taken from patients. This is a hospital-based observational study. Results: Dengue was the most common cause of febrile thrombocytopenia (50%) followed by malaria (23%). The other causes were viral fever (19%), scrub typhus (4%), mixed dengue and scrub typhus (2%), septicemia (2%). The patients were in the age group 16-80 years with 60 male and 40 females. Maximum patients (76%) were found to have thrombocytopenia in the range of 50,000-1,50,000/cumm, 16 cases had thrombocytopenia in the range of 20,000-50,000/cumm while 8 cases had thrombocytopenia in the range of <20,000cumm. bleeding manifestations were very rarely seen as present in 3 cases (3%) with petechiae as the commonest bleeding manifestation (2%). Severe thrombocytopenia was seen in dengue fever and falciparum malaria. Mortality was observed in 2 cases (2%) and multiorgan dysfunction was present in all those 2 cases. Conclusion: Dengue is the commonest cause of febrile thrombocytopenia and the severity of thrombocytopenia was not associated with increased mortality but mortality was due to multiorgan dysfunction.