Diversity patterns of aquatic insects among sampling sites lying with!ç the unprotected and protected areas of Western Ghats were studied. This study primarily emphasizes whether anthropogenic influence is the prime cause for the presence of aquatic insects especially of pollution-sensitive organisms belonging to the orders Ephemeroptera, Plecoptera and Trichoptera, or to factors such as the physico-chemical features of the water, or sampling methods. Six streams were sampled quantitatively, of which three streams (Abbifalls, Monkey falls and Silver Cascade) were within protected areas and the remaining three streams (Kumbakarai, Shenbagadevi and Manimutharu falls) were in unprotected areas. A total of 3,209 individual aquatic insects belonging to 25 genera, 18 families and 7 orders were collected. The highest species richness and abundance was observed in Monkey falls followed by Kumbakkarai falls. Large numbers of more habitat-sensitive organisms such as Ecdyonurus sp., Epeorus sp., Thalerosphyrus sp., Euthraulus sp., and Nathanella sp., were found in Monkey falls. Though the species assemblage was somewhat different, pollution-sensitive taxa were also observed in Kumbakkarai falls. Shenbagadevi and Manimutharu falls had a lower diversity of aquatic insects. The likely causes of these differences are discussed.