The hitherto unknown male, pupa and fourth instar larva of Culiseta atlantica (Edwards, 1932) are described, based on the examination of 25 males, 31 associated pupal exuviae and 77 larvae caught by the writers from rockpools in the bed of the Ribeira do Salto River, east of the town Ribeira Grande, S. Miguel Island, Azores. Diagnostic characteristics of the adults (external morphology), male terminalia, pupa and fourth instar larva of Cs. atlantica and the closely related species Cs. annulata (Schrank), Cs. incidens (Thomson), Cs. particeps (Adams) and Cs. subochrea (Edwards) are given and identification keys are provided.