Infant colic, excessive crying of unknown cause, is a major burden to families and effects about 10-30 % of infants. Despite decades of research, the exact cause and treatment of infant colic has remained elusive. The use of Lactobacillus reuteri (DSM 17938) in infant colic is somewhat controversial and hence, we designed this study to evaluate its efficacy in infantile colic. We recruited predominantly or exclusively breastfed infants, aged less than 4 months in a placebo controlled observational randomized study. Participants' were assigned to receive L. reuteri at a dose 10(8) colony forming units (n = 21) and placebo (n = 21). Placebo was an identical formulation without live micro-organisms. Treatment was given to subjects for 21 days and they were followed for 4 weeks. Treatment success (primary outcome), daily reduction in crying time, parent satisfaction and reduction in maternal depression (secondary outcomes) were assessed at the end of study period. Treatment success was observed in all infants (100 %) of the probiotic group while it was seen in 15.7 % of the placebo group. Mean daily crying time was more significantly reduced to 32.1 ± 8.3 min/day (P < 0.01) from 200.9 ± 6.3 min/day in the probiotic group as compared to the placebo group (120.6 ± 20.0 min/day). Moreover, throughout the study period, parent's satisfaction and improvement in maternal depression (Edinburgh postnatal depression scale) was also significantly higher in the probiotic group. In our study population, reduction in crying time was significant (P < 0.01) even during first week of initiation of therapy. We conclude that L. reuteri (DSM 17938) reduces daily crying time and maternal depression during infantile colic. We suggest L. reuteri may be a safe and efficacious option for reducing infant colic.