The review considers the fundamental biological problem of fungal dimorphism as an adaptive reaction to adverse impacts. Primary attention is paid to sterols, phospholipids, storage lipids, and fatty acids. The structural and biological functions of sterols are considered, as well as their role in membrane stabilization under stress and their relation to morphogenetic processes in mycelial fungi, of which many are pathogenic. Data on the biosynthesis of the main fungal sterol, ergosterol, are presented, as well as data on the inhibitors of this process and on the mutants deficient in its particular stages. Ergosterol biosynthesis is also considered in terms of its relation to the composition of the fungal cell wall, which is the cell shape-determining structure, and to the intensity of chitin synthesis, a process in which azole derivatives play a role. Data obtained by the authors are presented that show the role of changes in the composition of sterols, phospholipids, storage lipids, and unsaturated fatty acids of resting cells in the induction of yeastlike growth in mucoraceous fungi.