Human beings and gut microbiota are in a symbiotic relationship, and the hypothesis of a "super organism" composed of the human organism and microbes has been recently proposed. The gut microbiota fulfills important metabolic and immunological tasks, and the impairment of its composition might alter homeostasis and lead to the development of microbiota-related diseases. The most common illnesses associated with alterations of the gut microbiota include inflammatory bowel disease, gastroenteric infections, irritable bowel syndrome and other gastrointestinal functional diseases, colorectal cancer, metabolic syndrome and obesity, liver diseases, allergic diseases, and neurological diseases such as autism. In theory, every disease associated with the impairment of intestinal microflora might benefit from the therapeutic modulation of the gut microbiota. A number of attempts to manipulate the microbiota have not produced identical results for every disease. Although antibiotics and probiotics have been available for a long time, the so-called fecal microbiota transplantation, which is a very old remedy, was only recently re-evaluated as a promising therapeutic approach for microbiota impairment. A comprehensive understanding of the gut microbiota composition, in states of both health and various diseases, is needed for the development of future approaches for microbiota modulation and for developing targeted therapies. In this review, we describe the role of the microbiota in several diseases and the related treatment options that are currently available.