Chromosome numbers are reported for 73 collections of grasses from the states of Yucatán, Campeche, Oaxaca, and Chiapas in Mexico and in Colombia from Amazonas, Caquetá, and Cundinamarca. Included in the reports are counts for 61 species representing 31 genera. The first chromosome records are reported for the genera Hymenachne and Neurolepis, and the following 25 species: Bothriochloa schlumbergeri, Chloris inflata, Digitaria obtusa, Eragrostis acutiflora, E. domingensis, E. maypurensis, E. trichocolea, Eriochloa aristata, Homolepis aturensis, Hymenachne donacifolia, Ichnanthus axillaris, I. breviscrobs, I. tenuis, Lasiacis ruscifolia, L. sorghoidea, Muhlenbergia tenella, Neurolepis aperta, Olyra loretensis, Panicum mertensii, P. pulchellum, P. sellowii, Paspalum orbiculatum, Pereilema crinitum, Setaria poiretiana, and Sporobolus jacquemontii. Counts differing from those previously reported are given for Chloris chloridea, Eragrostis viscosa, and Paspalum paniculatum.