The Atlantic Forest of Brazil has been identified as a biodiversity hotspot of global significance. We assessed chironomid (Diptera:Chironomidae) taxa richness in 2 vegetation types in this region: the Atlantic Rain Forest and the Atlantic Semi-deciduous Forest. Taxa were collected from 15 low-order streams across multiple habitats. A total of 191 morphospecies were recognized (125 Chironominae, 28 Tanypodinae, and 38 Orthocladiinae). We estimated chironomid richness using a Bayesian statistical approach. Species-richness estimates ranged from 200 (credibility interval, 195–207) to 267 (248–288). These results place low-order streams from Atlantic Forest among the most chironomid speciose areas in the world.