Objectives: The present study aimed at evaluating factors affecting scar formation and tuberculin skin test (TST) response in Bacillus Calmette-Guerin (BCG) vaccinated infants. Methods: In the current study, 216 infants with gestational age (GA) of 26 to 40 weeks and birth weight of 730 g to 4590 g were included. The mean corrected age was 6.27 ± 3.79 weeks, and the mean weight was 4442.4 ± 1084.1 g (range 2100 - 7700 g) at the time of BCG vaccination. TST was applied at 8 to 16 weeks of vaccination. Factors affecting TST response and BCG scar formation were evaluated. Results: A scar response to BCG vaccination was found in 60%, 49.4%, and 59.7% of the infants with GA 2500 g, 1500 - 2500 g, and 10 mm developed scars ≥ 2 mm (r = 0.360; P = 0.001). Conclusions: Prematurity or birth weight does not affect BCG scar formation. TST response is lower in preterm babies. The correlation between scar formation and TST response was too low to be interpreted as positive.