Our objective was to evaluate incidence, duration of illness, and anthropometrics in children who received a nutritional supplement with or without synbiotics. A double-blind, randomized study was done with 1-6 year old children who were between -1SD and -3SD from the median of weight-for-height. Children received a nutrition supplement with (N=310) or without (N=316) synbiotics. The number of sick days per month decreased over four months for both groups (p<0.001), being more pronounced in 1 to 2 year old children (p<0.001). The synbiotic group experienced fewer constipation days (p=0.02) and both feeding groups experienced improved anthropometric measures (p<0.001). Underweight children, receiving an average of 40 mL/kg/day of a nutritional supplement, experienced catch-up growth and fewer sick days. The synbiotic group experienced a significant reduction in constipation among all ages and significantly reduced sick days among 3 to 5 year old children.