The species–area relationship was used to test the effects of habitat reduction on the proportion of tetrapod species that would be considered threatened with extinction, assuming the current estimate of 19% of remaining forest coverage in Rio de Janeiro State, Brazil. Here, species–area estimates from deforestation were compared with a Red List produced by experts. Analyses were performed with: (1) the total pool of species that occur in Rio de Janeiro State (159 amphibians, 115 reptiles, 635 birds and 157 mammals); (2) the pool of species endemic to the Atlantic forest (109 amphibians, 46 reptiles, 149 birds and 35 mammals). The sensitivity of the analyses to variations in the Z parameter of the species–area relationship was evaluated. In general, the species–area overestimated the total number of species threatened with extinction for all tetrapods, while the estimate of endemic mammals predicted to be extinct was close to the number of endemic species listed as threatened with extinction. Furthermore, changes in the Z-values did not affect those results. The species–area relationship accurately predicted the number of endemic birds assumed to be extinct since it used values of Z smaller than 0.25. The analyses with endemic species of reptiles and amphibians of Atlantic forest overestimated the number of species predicted to be extinct for both groups. In conclusion, at the considered scale, mammals and birds endemic to the Atlantic forest seem to be more affected by deforestation than reptiles and amphibians.