Summary. Based solely on molecular markers, D-D3 28R rDNA and ITS1, Longidorus intermedius and L. piceicola share a high level of similarity. However, despite this molecular similarity, L. piceicola and L. intermedius significantly differ in morphometrics and ontogeny. Two key concepts in the development and growth of longidorid nematodes are developmental and growth patterns. Developmental patterns categorize longidorid nematodes according to whether they undergo four or three juvenile developmental stages (JDS) during post-embryonic development. Growth patterns refer to specific morphometric levels, which are more or less similar between species within a genus with the same developmental pattern. There are some differences between different populations of the same species, probably due to intraspecific variability and the environmental conditions in which they live. Longidorus piceicola undergoes four JDS, while L. intermedius undergoes three JDS. In the typical life cycle of longidorid nematodes, there are four or three molts, which occur between the four or three JDS, with the last molt preceding the fully sexually mature adult stage. The similarities and differences between these two developmental patterns are not well known. Growth patterns refer to changes in specific morphometric dimensions during the post-embryonic growth of a nematode, such as: body length, odontostyle and replacement odontostyle size, and body volume. Using these characteristics, a study was conducted to assess whether there are similarities or differences between selected populations of Longidorus piceicola (4 JDS) and L. intermedius (3 JDS). This paper presents results on the developmental and post-embryonic growth patterns of the species Longidorus piceicola and L. intermedius.