PURPOSE: Congenital adrenal hyperplasia(CAH), which is classified into salt-wasting, simple virilization and non-classic type according to clinical features, is difficult to detect in early stages. Failure to diagnose it in the initial state may lead to life-threatening adrenal crisis, inappropriate male sex assignment in the genetic female, acceleration of skeletal maturation and subsequent short stature. Therefore, we studied the variables increasing the 17-hydroxyprogesterone(OHP) values for more specific and sensitive diagnosis of CAH. METHODS: We classified 3,532 newborns into variable factors; gestational age, birth weight, gender, delivery type, sampling date and stress. Then, we analysed the relationships between 17-OHP values and variable factors. RESULTS: The mean value of 17-OHP was 4.21+/-0.03ng/ml. There were significant differences among the variable factors except gender. The mean value of male was 4.26ng/ml, and that of female was 4.15ng/ml(P=0.10). The mean value of 17-OHP in vaginal delivered newborn was higher than C-section delivered ones(4.71ng/ml, 3.34ng/ml, P=0.0001). It was also higher in low birth weight(P=0.0001), in prematurity(P=0.001), those sampled within 4 days(P=0.0001), stressful condition and ventilator care-assisted(P=0.004). CONCLUSION: 17-OHP value in neonatal screening is influenced by several variables such as vaginal delivery, ventilator management, low birth weight, sampling date and prematurity. If the 17-OHP value is increased, we have to consider the variables influencing the increase in value and follow up with time interval or analysis of genetic mutations.