Adult resting habits and breeding habits of Anopheles nigerrimus in Sri Lanka were investigated. This species is primarily exophilic, in contrast to endophilic An. culicifacies in the same areas. An. nigerrimus larvae were found in all habitat types sampled, in particular paddy fields where a large quantity of agricultural pesticides is used. This species was shown to be resistant to a range of insecticides including a number of organophosphates and carbamates. The adult resting behaviour precludes selection of resistance from indoor residual insecticide usage for malaria control and suggests selection from agricultural pesticide usage.