A dengue outbreak occurred in Kaohsiung City starting in July in 2001. We studied the clinical profile of all patients admitted to Kaohsiung Veterans General Hospital during this outbreak from July 2001 to January 2002. A total of 25 cases of clinically suspected dengue fever were treated during this period, and 13 of them were confirmed by laboratory results (13/25; 52%). Eleven of the 25 patients (11/25; 44%) were admitted. The mean age of the patients with laboratory confirmation of infection was 53 years (range, 7 to 85 years). Headache (7/13; 53.8%), bone pain (8/13; 61.5%), myalgia (10/13; 76.9%), abdominal pain (7/13; 53.8%), and skin rash (9/13; 69.2%) were the most common presentations. A high proportion of patients were classified as having dengue hemorrhagic fever (DHF) [6/13; 46.2%] and 2 of these patients had dengue shock syndrome (DSS) based on the World Health Organization criteria. Pretibial petechia (6/13; 46.1%), gastrointestinal bleeding (6/13; 46.1%), and hemoptysis (4/13; 30.8%) were the most common hemorrhagic manifestations. The average hospital stay was 7.1 days. Thrombocytopenia was very common and 84.6% patients had a platelet count less than 100,000/mm3. Monocytosis was found in all patients. Few patients required blood or platelet concentrate transfusion. The 2 patients who developed DSS both survived. All patients recovered completely without any obvious sequela. In conclusion, there was a high percentage of DHF among patients in the dengue outbreak in 2001. Increasing rates of DHF compared to previous reports from Taiwan may be a sign of hyperendemicity (multiple serotypes present) of the dengue virus in Kaohsiung City and its greater likelihood elsewhere in Taiwan. Prevention and control of both dengue fever and DHF have thus become increasingly important.