Despite unproven effectiveness, Lactobacillus acidophilus is a widely used probiotic in the treatment of pediatric diarrhea. In this report, we evaluated the association between length of stay (LOS) for 290 young children hospitalized with acute diarrhea and adjuvant therapy with a probiotic mixture containing 80% L acidophilus that was included in treatment for 22.4% of them. Overall, no association between LOS and use of L acidophilus was recorded after controlling for age, length of diarrhea symptoms, duration of intravenous fluids, and prior exposure to antibiotic. However, LOS was directly associated with use of L acidophilus in children with negative stool studies, and no such association was recorded in children with positive stool for rotavirus or other infections. We concluded that adjuvant therapy with L acidophilus mixture is not beneficial for young children hospitalized with acute diarrhea.