The objective of the study was to evaluate the efficacy of a health check-up program among Thai people at the National Cancer Institute in the years 2008-2009. The program included history taking, physical examination, chest X-ray, EKG, and laboratory tests. A total of 28,240 women and 9,665 men were included in the study, with mean ages of 44.5 and 46.9 years, respectively. The study showed that obesity, as assessed by a BMI over 25.0 kg/m2, in men and women was present in 41.4% and 30%, respectively. Biochemical study revealed that anemia was prevalent in 21.6% of men and 20.1% of women. High plasma glucose level (>115 mg/dL), cholesterol level (>200 mg/dL), triglyceride level (>190 mg/dL) in men was 13.8%, 63.8%, 22.6% and 7.7%, 61.1%, 8.9% in women. Hepatitis B virus infection was found 7.5% in men and 4.1% in women. In this study, 177 new cancer cases were detected, of which 35 were breast, 19 were cervical and 26 were colorectal, most of these cancers being detected at early stage. In addition, precancerous states was also found including 718 cases of benign and 99 cases of adenoma in situ. In conclusion, an annual check up may detect abnormalities that have no obvious clinical symptoms of disease. Early detection of asymptomatic neoplasms and precursor lesions should contribute to a prompt provision of treatment and further decline of death from cancer.