The U3 snoRNA is an exceptional box C/D snoRNA, which is involved in pre-rRNA processing without directing chemical modifications. We report here on a comprehensive computational survey resulting in U3 sequences for more than 90 additional eukaryotes. This extended data basis is used to improve the secondary structure models. The detailed investigation of the structural variation of U3 snoRNAs turns out to be much more extensive than previously thought. Many fungal U3 genes, in addition, contain introns. U3 promoters are snRNA-like but show substantial variations even between related species.