OBJECTIVES:  The population at risk for herpes zoster (HZ) is increasing with prolonging life expectancy in Hong Kong. HZ treatment cost data are essential to assist the cost-effective implementation of zoster vaccination program. We aimed to describe HZ clinical outcomes and direct cost in older adult patients treated in Hong Kong inpatient and outpatient settings. METHODS:  A retrospective, observational study was conducted in two clusters of Hospital Authority, the largest public healthcare provider in Hong Kong. Medical records of patients aged ≥50 years with HZ diagnosis at outpatient clinics and general hospitals in January 2011 to December 2013 (prior to zoster vaccine became available in Hong Kong) were reviewed. Outcome measures included HZ-related length of hospital stay (LOS), outpatient visits, treatment cost, and HZ-related complications. RESULTS:  We reviewed 215 HZ cases (46% male; age 70±12 years), 102 (47%) were hospitalized patients and 113 (53%) were outpatient cases. Of the 102 inpatient cases, 15 (15%) were immunocompromised patients. Median LOS was 4 days (IQR 3-8) days. HZ-related complications occurred in 47 (46%) inpatient cases. Median inpatient treatment cost was HKD21,630 (IQR HKD15,030-38,430) (USD1=HKD7.8). Inpatient cost for immunocompromised patients (HKD49,990; IQR HKD26,125-90,310) was significantly higher than non-immunocompromised cases (HKD20,095; IQR HKD15,030-33,750) (p<0.001). Immunocompromised patient was associated with high (≥75^th percentile) inpatient treatment cost (OR 8.88; 95%CI 2.67-29.55; p<0.001). For the 113 outpatient cases, 26 (23%) patients were immunocompromised. 58 (51%) patients used one-time outpatient clinic service and 55 (49%) patients had 4.9±3.2 clinic visits for HZ treatment. Outpatient treatment cost (HKD1,100; IQR HKD1,100-4,785) was significantly lower than inpatient treatment cost (p<0.001). There was no significant different between the outpatient treatment costs in immunocompromised and non-immunocompromised patients. CONCLUSIONS:  Inpatient HZ treatment cost was substantially higher than outpatient cost. Immunocompromised patient was associated with high inpatient HZ treatment cost in older Hong Kong adults.