This paper, treating the tortricid subfamily Chlidanotinae (comprised of Chlidanotini, Hilarographini, and Polyorthini), represents the first in a proposed three-part series examining variation in the number of bristles in the frenulum of female tortricid moths. Based on an examination of 86 described species and 11 undescribed species representing 31 genera of Chlidanotinae, the vast majority of females of Chlidanotini and Hilarographini have a two-bristled frenulum, whereas a three-bristled frenulum is the more common state in Polyorthini. When the character states are mapped on a composite, schematic phylogeny of the subfamily, the change from three to two bristles appears to have evolved once at the base of the Chlidanotini Hilarographini clade and twice within Polyorthini. The consistency of this character within Chlidanotini and Hilarographini provides further evidence for the exclusion of Mictocommosis Diakonoff, Mictopsichia Hübner, and Tortrimosaica Brown and Baixeras from Hilarographini. The distribution of the two-bristled frenulum in Polyorthini appears to support one major clade identified by Razowski (i.e., Ardeutica Meyrick, Polyortha Dognin, Pseudatteria Walsingham, Polythora Razowski), plus one outlier, Cnephasitis Razowski. In the monotypic Olindia schumacherana (Fabricius), five of 18 representatives examined had two bristles, whereas the remainder had three. Minor deviations from this pattern appear to represent intraspecific variation. Preliminary investigations of the character in other tortricid subfamilies suggest a high degree of variation within tribes, genera, and species, with asymmetry common in many individuals. In contrast to the situation in most tortricid taxa, we conclude that variation in the number of bristles in the frenulum is phylogenetically informative in Chlidanotinae.