Probiotics are live microbial food supplements or components of bacteria, which have been shown to have beneficial effects on human health. Probiotic bacteria are used to treat or prevent a broad range of human diseases. Different species of microorganisms such as lactic acid bacteria or yeasts have been proposed for human use. Probiotics could be used for several conditions such as diarrhea, irritable bowel syndrome, urinary tract infections, immune disorders, cancer, Helicobacter pylori, lactose intolerance, hyper cholesterolaemia, inflammatory bowel disease and allergy. The aim of this review is to consider the current evidence on the effects of probiotics on human health.