OBJECTIVES: To describe clinical characteristics and treatment outcomes and to document adaptation of medical services of COVID-19 cases receiving care at Bangkok Hospital Headquarters (BHQ) from January to May 2020. MATERIAL AND METHODS: Clinical and laboratory data of confirmed COVID-19 cases were collected using the case record form designed by the clinical team providing care to suspected and confirmed COVID-19 cases. Data were analyzed for clinical characteristics and treatment outcomes. In parallel, the Infection Control Nurse (ICN) team gathered and summarized data on hospital responses, including statistics of hospital staff exposed to COVID-19 cases and their clinical symptoms and test results. RESULT: From January to May 2020, Bangkok Hospital Headquarters provided COVID-19 screening test using RT-PCR to 2,362 patients, of which 40 (1.69%, 95%CI 1.61%, 1.78%) were positive. Upon diagnosis, two cases wanted to stay in other hospitals. Among 38 cases, the majority (63.0%) had no or mild symptoms, while a quarter (28.9%) had moderate and a few (7.9%) were severely ill. Common symptoms that presented among more than half of the cases were fever (79%), cough (71%), myalgia (58%), rhinitis (55%) and body pain (52%). Anosmia or hyposmia was reported among a third (37%) and ageusia among a quarter (21%). All moderate to severe cases had abnormal chest x-ray on arrival. Focal or patchy infiltration was found among mild to moderate cases. Among advanced or severe cases, chest x-Ray showed bilaterally diffused ground glass infiltration. Compared with asymptomatic or mild symptoms, cases with moderate to severe symptoms had significantly lower neutrophils (p = 0.018) and lymphocytes (p = 0.039) counts. Among 11 moderately ill cases, seven (64%) developed more severe symptoms during admission. In summary, among 38 COVID-19 confirmed cases receiving care in our hospital, half (19/38, 50%) recovered, 15 cases (39.5%) improved, two cases (5.3%) were transferred to other settings and one (2.6%) died. Hospital’s adaptation to the epidemic was in line with national protocols. A “war room” was established and 11 guidelines were created. Responses started from the first week of January 2020 before the first case in Thailand was detected. With strong preventive measures, there was no COVID-19 transmission from patients to health care workers. Among 117 high-risk close contact staff, 27 (23.0%) and 21 of 441 low-risk close contact staff (4.8%) had fever or upper respiratory track symptoms. All of the low-risk close contact staff tested negative for COVID-19 according to national standards set by Department of Disease Control. Only one of 117 high-risk close contact staff tested positive (0.9%). This staff was a computer technician sitting closely with a confirmed case who contracted COVID-19 outside of hospital. CONCLUSION: Although we were only a small part of the national response, what we learned was meaningful. Clinical and management teams are confident that if another wave of COVID-19 occurs, the hospital will be able to respond immediately using the existing knowledge and experience that was gained.