OBJECTIVE To evaluate evidence for probiotic efficacy for maintaining remission of ulcerative colitis (UC) in adults. METHODS A MEDLINE search (1948-November 2009) was conducted using ulcerative colitis and probiotics as terms for identifying pertinent studies. Search limits included English language and humans. Additional information was obtained from bibliographies. METHODS Prospective trials published in English and conducted in adults were included. Two open-label and 3 double-blind randomized trials evaluated probiotic efficacy for maintaining remission of UC. Clinical and surrogate markers for maintaining remission of UC were assessed. RESULTS A relationship between immune response and gastrointestinal microbials appears to be involved in the mechanism of UC. Trial results comparing the probiotic Escherichia coli Nissle 1917 to mesalazine have reported equivalent rates of UC relapse. Treatment with Lactobacillus rhamnosus GG strain alone or in combination with mesalazine resulted in a nonsignificant odds ratio decrease for relapse and a significant increase in time to relapse compared to treatment with mesalazine alone. Additionally, bifidobacteria-fermented milk-supplemented patients had significant reductions in UC exacerbations when compared to nonsupplemented patients. Probiotics were well tolerated, with adverse event rates similar between treatments. CONCLUSIONS Studies evaluating probiotics for maintaining remission of UC are limited by trial design and use of different probiotics with variable bacterial contents. Thus, questions remain regarding optimal probiotic, dosing, specific patient populations, and placement in therapy. To answer these questions, large, randomized, controlled trials need to be conducted before probiotics can be routinely recommended for maintaining remission of UC.