Stem cells are seen as a possible solution for organ and tissue regeneration and for the treatment or even cure of various diseases. There are basically two types of stem cells: embryonic and adult stem cells. Embryonic stem cells are derived from embryos and exhibit an extensive multiplication and differentiation potential. On the other hand, adult stem cells, which are found in bone marrow and other tissues, have a lower multiplication and differentiation capacity but are more easily isolated and applied. In adult stem cell therapies using bone marrow or umbilical cord blood transplantation, the differentiation of a certain cell type is induced and its multiplication is stimulated, followed by the implantation of these cells into damaged tissues. Examples of the application of stem cells include the treatment of autoimmune diseases such as type 1 diabetes mellitus and heart diseases. Stem cells open up new prospects for the treatment of a series of diseases. In this respect, basic knowledge of the mechanisms of growth and differentiation of these cells is of the utmost importance to optimize therapeutic results. In this review, we discuss the mechanisms of stem cell differentiation and describe the clinical results reported in the literature, mainly by Brazilian research groups.