The importance of many of Mexico's wetlands for waterbirds remains poorly assessed, and this is an obstacle in planning their conservation. Between Marismas Nacionales, Nayarit, and the center of the state of Guerrero, a span of roughly 1150 km on the Pacific coast of Mexico, there is only large coastal wetland: Laguna de Cuyutlán and its associated wetlands in the state of Colima. We studied the waterbirds that used this area during the non-breeding season, from September 1996 to March 1997. We surveyed birds on eight occasions from 11 stations that included different combinations of mudflats, water pools, shallow water, deep water, and mangroves. Throughout the study we counted 54,370 individuals of 57 species of waterbirds, but 11 species accounted for 90% of all individuals. The total number of individuals exhibited strong seasonal variation, although peaks in abundance reflected variations of only a few species. Waterbirds differed greatly in their use of different sites. The site with the most individuals, but not with the most species, had a combination of mudflats, shallow water, and deeper water. The poorest sites where those associated with a thermoelectric facility. We cannot extrapolate our numbers to the entire wetland complex, but the overall numbers of waterbirds suggest that the area be considered an Área de Importancia para la Conservación de las Aves. The two economic activities in Cuyutlán, fishing and salt production, do not seem to pose direct threats to waterbirds.