We describe the frequency of occurrence and seasonal variations of shorebirds (Charadriidae and Scolopacidae) along a 120-km transect of beach between Balneário Pinhal and Mostardas north of Lagoa do Peixe National Park, Rio Grande do Sul State over a 2-year period (Oct 2007 to Sep 2009). A total of 96,889 shorebirds was recorded. The greatest abundance occurred between October and April and the lowest occurred between May and September. The most abundant of the 17 species recorded were Sanderlings (Calidris alba), White-rumped Sandpipers (C. fuscicollis), and Red Knots (C. canutus). The least abundant were Semipalmated Sandpipers (C. pusilla), Rufous-chested Plovers (Charadrius modestus), and Hudsonian Godwits (Limosa haemastica). Fourteen species were migrants from the Northern Hemisphere, one was a migrant from the Southern Hemisphere, and two were residents. Nine species were recorded regularly, two were recorded sporadically, and six were recorded occasionally. Six Nearctic species were recorded in June and July most likely indicating the presence of non-breeding immatures. The beaches of Rio Grande do Sul are important migration stopover and wintering sites for many shorebirds in southern Brazil and should be a focus of conservation efforts, especially given the increasing development pressure that threatens these areas.