Small untranslated RNA genes transcribed by RNA polymerase III (class III genes) account for a substantial part (about 10%) of the mammalian genome. In addition to the well-known 5S rRNA, tRNA, and 7SL RNA genes and short interspersed elements (SINEs), class III includes several new genes, whose function is poorly understood. The expression regulation mechanisms substantially differ among class III genes on recent evidence, suggesting their gene, tissue, and cell state (resting, stress, apoptosis) specificity. The review considers the known genes for small untranslated RNAs, possible mechanisms regulating their expression (with the example of some SINEs), and the role of their transcripts in regulating cell processes.