Numeral-incorporating roots in the numeral systems of Argentine Sign Language (LSA) and Catalan Sign Language (LSC), as well as the main features of the number systems of both languages, are described and compared. Informants discussed the use of numerals and roots in both languages (in most cases in natural contexts). Ten informants took part in the LSC data collection, and six in the LSA data collection. The data were corroborated by analyzing the videos available at www.youtube.com/confargsordos (for LSA) and by videos and books provided by the ILLESCAT Foundation (for LSC), as well as by previous research. A general inventory of roots in both languages and specifically of roots in both numerals systems was carried out. The role of roots in the formation of ordinals and cardinals and the main features of both number systems are described. The data suggest that numeral-incorporating roots in these number systems are formed only from numerals that do not derive from manual counting. This assumption is discussed, and further research about this point is emphasized. © 2010 Project MUSE®.