IMPORTANCE Excessive infant crying is common, distressing, but without proven effective prevention or management options. Probiotics may be a promising solution. OBJECTIVE To examine whether probiotics are effective in the prevention/management of crying ("colic") in infants 3 months or younger. DATA SOURCES A systematic search of MEDLINE, EMBASE, and the Cochrane Library, supplemented by the metaRegister of Controlled Trials. STUDY SELECTION Studies that randomized infants 3 months or younger to oral probiotics vs placebo or no or standard treatment with the outcome of infant crying, measured as the duration or number of episodes of infant crying/distress or diagnosis of "infant colic." Twelve of the 1180 initially identified studies were selected. DATA EXTRACTION AND SYNTHESIS This review/meta-analysis was conducted according to guidelines from the Cochrane Handbook for Systematic Reviews of Interventions, with reporting following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Data were independently extracted by 3 of us. MAIN OUTCOME(S) AND MEASURE(S) Infant crying, measured as the duration or number of episodes of infant crying/distress, or diagnosis of "infant colic." RESULTS Of the 12 trials (1825 infants) reviewed, 6 suggested probiotics reduced crying, and 6 did not. Three of the 5 management trials concluded probiotics effectively treat colic in breastfed babies; 1 suggested possible effectiveness in formula-fed babies with colic, and 1 suggested ineffectiveness in breastfed babies with colic. Meta-analysis of 3 small trials of breastfed infants with colic found that Lactobacillus reuteri markedly reduced crying time at 21 days (median difference, -65 minutes/d; 95% CI, -86 to -44). However, all trials had potential biases. Meanwhile, of 7 prevention trials, 2 suggested possible benefits. Considerable variability in the study populations, study type, delivery mode/dose of probiotic supplementation, and outcomes precluded meta-analysis. CONCLUSIONS AND RELEVANCE Although L reuteri may be effective as treatment for crying in exclusively breastfed infants with colic, there is still insufficient evidence to support probiotic use to manage colic, especially in formula-fed infants, or to prevent infant crying. Results from larger rigorously designed studies applicable to all crying infants will help draw more definitive conclusions.