O-Glycosylation in many fungal species is initiated in the endoplasmic reticulum by protein mannosyltransferases (Pmt-proteins), which transfer mannose to serine or threonine residues, and it is completed by mannosyltransferases (Mnt-proteins) in the Golgi. In this review, some recent results on O-glycosylation in the human fungal pathogen Candida albicans are discussed and compared to the corresponding knowledge in the non-pathogenic yeast Saccharomyces cerevisiae. The Pmt-family in C. albicans comprises five isoforms, of which Pmt1p and Pmt6p have been studied in detail. Surprisingly, O-glycosylation mediated by Pmt-proteins is required not only for the modification of several secreted and cell-wall proteins, but also affects yeast-hyphal morphogenesis (dimorphism) and resistance to several antifungal compounds. Furthermore, Pmt1- and Pmt6p-activities maximize adherence to host cells and determine or contribute to virulence in models of systemic infection. Thus, O-glycosylation processes directly and/or indirectly affect several virulence traits of C. albicans and can be considered as potential antifungal targets.