Probiotic milk has been previously demonstrated to reduce the number of respiratory infections (RI) among children attending day care centres. Thus, this pilot study was aimed to assess the efficacy and the safety of 3 month treatment with Bacillus clausii in the prevention of recurrent respiratory infections (RRI) in children. Eighty children with RRI were studied: 40 of them were randomly treated with B. clausii for 3 months, and followed up for further 3 months; 40 were included in the control group during the same period. Children treated with B. clausii had shorter duration of RI in comparison with the control group both during the treatment phase (mean 11.7 days vs 14.37; p=0.037) and the follow-up period (mean 6.6 days vs 10.92; p=0.049). This effect was evident also in allergic children during the follow-up. In conclusion, this pilot study provides the first preliminary evidence that B. clausii may exert a significant and persistent impact on RI in children and is safe and well tolerated.