The discussion of factors predisposing to oral yeast infections is very important, and we can ask: what is primary and what is secondary? Without predisposing factors it is difficult to have oral yeast infections, and a yeast infection may also be the first sign of a developing basic illness. As long as the predisposing factors cannot be eliminated, recurrences of oral yeast infections are to be expected. We can say that local and systemic factors permit this microorganism to cause disease and that it is extremely rare to find a case of oral candidosis in which one or more of these factors cannot be identified. There are many kinds of lists in the textbooks and some review articles in the literature, but more research is needed for better understanding of factors predisposing to oral yeast infections.