We carried out an assessment of the resistance of 71 accessions of cotton (Gossypium spp. L.) to the aphid Aphis gossypii and to leafhoppers under natural infestation. Our objectives were (i) to improve the methods for screening cotton germplasm for resistance to both pests, and (ii) to test the existence of genetic correlation between resistances to both insects. For both insects, the percentage of colonized leaves exhibited high genotypic correlation with the number of insects per leaf, had similar or higher heritabilities, and appeared as the better measure of insect populations. The one-plant-per-plot experimental design used allowed an assessment of resistance with high heritability value, and proved to be suitable for the screening of cotton germplasm. G. arboreum was more resistant to both insects than G. barbadense and G. hirsutum. While hairiness had a significant negative effect on resistance to aphids, no significant effect was observed on resistance to leafhoppers, excepted in G. arboreum. The lack of genotypic correlation between resistance to aphids and to leafhoppers demonstrated that a simultaneous improvement of the resistance is possible.