1. World wide, and in Australia, many frog populations have declined over the last two decades. The present study was undertaken to determine whether urbanization has affected frog diversity and abundance. 2. Five urban sites were paired with non-urban sites. Urban sites were in Katoomba and Blackheath, and were subject to physical environmental disturbance and impacted by storm water pollution due to urban runoff. Non-urban sites were in the Blue Mountains National Park and were effectively subject to no human impact. 3. Water quality at urban sites was typical of sites polluted with sewage, while non-urban sites exhibited water quality typical of 'pristine' natural bushland streams. 4. Six species were found at urban sites (Litoria peronii, Litoria dentata, Litoria verreauxii, Limnodynastes dumerilii, Limnodynastes peronii, Crinia signifera), with up to four species present at a site. Only one species (C. signifera) was recorded at non-urban sites, and frogs were absent from most non-urban sites. 5. The situation in non-urban sites mirrors the trend of decline observed in other montane regions. Surprisingly, frog abundance and diversity were higher in urban habitats, running counter to this trend. 6. We hypothesize that the salts, detergents and other chemicals in urban wastewaters provide frogs with a level of protection against disease, particularly chytridiomycosis.