We studied the distribution of anurans in savanna, regrowth and mature forest at the mouth of the Tapajós river in Brazilian Amazonia. We sampled 31 sites on the right bank of the Tapajós river and on the shores of lakes nearby, and recorded all acoustic and visual observations of frogs. We found 18 anuran species: Leptodactylidae (8), Hylidae (7), Bufonidae (2) and Pseudidae (1). The distribution of species indicated that some species are generalists and others are restricted to certain habitats. The species at Alter do Chão are a subset of those found in forested sites in Amazonia. Lakes and forested areas had the greatest anuran diversity, but are also the areas most disturbed by tourist development and agriculture. Reduction of anuran diversity in the area could be minimized by concentrating development along the main beaches of the Tapajós river.