- To determine the impact of probiotics on the prevention of problems with bowel movements malnutrition and infection. A randomized, double-blind, placebo-controlled trial. Peripheral Geriatric Hospital. 243 elderly patients age ≥ 65 y who were hospitalized in a Geriatric Orthopedic Rehabilitation Department. Intervention: Participants were randomized into treatment or control groups (daily probiotics or placebo for 45 consecutive days, respectively). The main outcomes were: number of days of constipation or diarrhea and the number of days of laxative use. Secondary measures were nutritional status and blood measurements. Of 599 patients admitted to the Geriatric Rehabilitation ward, 345 were eligible and agreed to participate. During a 7-day pre-trial period, 102 patients dropped out (45 and 57 in the probiotic and placebo groups respectively). Out of the 243 patients who entered the study, 28 dropped out during the study (11.5%), leaving 215 patients. Throughout the 45 days of follow-up, the incidence of diarrhea was significantly lower among the study group (HR=0.42, p=0.04) with a more pronounced difference among participants aged ≥ 80 y (HR=0.32, p=0.026). Laxative use (as an indicator of constipation severity) was significantly lower in the study group compared with the control group (HR=0.74, p=0.032). Serum albumin, prealbumin and protein increased significantly more in the treatment group compared with the control group among participants age ≥ 80 y (P=0.047, p=0.07, p=0.03 respectively) but not in the younger age group. We showed that probiotic supplements may have a positive effect on bowel movements among orthopedic rehabilitation elderly patients.