The Aim of this study is to evaluate the effect of presumed risk factors on antiHBs response to vaccination in NICU graduates. The study group consisted of 150 infants (105 term, 45 preterm) who were discharged from the NICU. Hepatitis B vaccine was administered according to birth weight adjusted schedule. Infants with birth weight less than 2000 g were vaccinated at intervals of 0.1.2 and 12 months. Other infants were vaccinated with 0, 1, 6 months schedule. AntiHBs titers were studied 3 weeks to 2 months after the last vaccine dose. AntiHBs titers were classified into 4 groups as < 10mIU/mL, 11–99 mIU/mL, 100–999 mIU/mL, >1000 mIU/mL consequently. Distribution of the antiHBs levels of preterm infants were different than term infants (p<0.05). Antibody titers increased as birth weight and gestational age increased (p<0.05). AntiHBs titers were not different between the healthy term and sick term infants (p>0.05). Overall seroconversion rate was %97.3 (preterm 95.6%, term 98.05%). In four infants (2 preterm, 2 term) seroconversion were not sustained. Antibody response were not effected from the presumed risk factors such as fresh frozen plasma, IVIG, exchange transfusion, other blood products transfusions. Inflammatory processes such as sepsis, pneumonia, preterm rupture of membranes had no effect on the titers either. As a conclusion preventable levels of antiHBs were achieved in preterm and sick term infants with the schedule routinely used. We concluded that presumed risk factors and transfusion of blood products did not have negative effect on immune response to Hepatitis B vaccine.