The knowledge of the population dynamics and vertical distribution of insect pests in host plants are fundamental for the development of programs of integrated pest management. In the present work, a population survey of apterous cabbage aphid, Brevicoryne brassicae (L.), was carried out aiming to determine the period when this aphid reachs the highest population density and the within-plant distributions on its common host, kale, Brassica oleracea L. var. acephala DC., cultivated in Jaboticabal, State of São Paulo. The study took place during the 1998 and 1999 Brassica seasons, and limestone treatment was only made in the field cultivated in 1998. The cabbage aphid was sampled by visual search on leaves classified in three categories: top, middle and basal. In the two studied seasons, the B. brassicae infestations reached the highest population density in September, decreasing quickly afterwards. In the two fields, the same distributions of B. brassicae was not observed on top, middle and basal leaves. The factors that might have contributed to the differences observed in that distribution pattern were rainfall and magnesium limestone.