OBJECTIVE: To compare the BCG size in asthmatic and nonasthmatic children. METHODS: The size of BCG scar of two groups of children (the asthmatic group with a family history of some allergic disorder like asthma, atopic dermatitis, allergic rhinitis or allergic conjunctivitis in the first degree blood relatives and the control non asthmatic group with no history of any allergic disorder in the child or in the first degree blood relatives) of age 18 to 60 months having weight at or above 5th centile and BCG scar on right arm with a history of BCG vaccination in the first month of life, coming to a paediatric Clinic at Liaqatpur on every Friday and Sunday from October 2007 to July 2008, was measured and compared. RESULTS: Total 284 children were included for the study, 142 children in each group. The diameter of BCG scar was measured. 45.77% asthmatics compared to 31.69% nonasthmatics had BCG scar mark < or = 5 mm. The asthmatic patients demonstrated a 1.82 times greater risk of presenting a BCG scar diameter of < or = 5 mm when compared to the nonasthmatic group (odd ratio: 1.82; P = 0.0204). The mean (95% CI) diameter of BCG scar was 6.4mm (CI: 6.026082 to 6.775918 ) in the nonasthmatic group and 5.8mm ( 95% CI: 5.459303 to 6.146297) in asthmatic group. The difference was significant ( t test, P = 0.0204). CONCLUSION: Asthmatic children have smaller BCG scar as compared to nonasthmatic children.