OBJECTIVES: As elderly people tend to need more health care resources, a better understanding of the pattern of and factors affecting their health care use is needed.  This study aims to determine the pattern of and factors affecting health service utilization of elderly population in a province in Thailand. METHODS: A cross-sectional study was conducted using health insurance standard hospital data set (12-file data set), and standard health centers data set (18-file data set). All population aged 60 years or older who lived in Phitsanulok province in 2011 were included. Descriptive statistics were used to describe the demographic and health service utilization patterns of the patients, including out-patient visits and in-patients admission.   We performed two-part model to determine the factors associated with the use of health services. Logistic regression is used to predict the probability of using health care services, while negative binomial regression is used to explain the frequency of using these services. RESULTS: A total of 113,728 elderly populations living in Phitsanulok province in 2011 were included. The mean age was 70.18 with 55 % female. Eighty-seven percent of elderly population used health service at least once and forty-four percent visited multi-health-centers. One-third of elderly patients that used the health services were hypertension patients. Older age (incidence rate ratio: IRR 2.77; 95% confidence interval 2.75-2.79 for patients aged > 80 years), being female (IRR 1.96; 95% CI 1.95-1.98), and having multiple-comorbidities (IRR 1.56; 95% CI 1.40-1.73 for charlsons’ co-morbidities index [CCI] score of >4) increase the utilization of health service. CONCLUSIONS: Health need was the most important factor associated with health services utilization. Health system should be appropriately designed for elderly population. Further studies are needed to evaluate economic consequences of the elderly’s health utilization and identify the factors affecting patients who visit multi-health-centers.