ENThis study is based on the longitudinal corpus data of two Lithuanian children (1;7–2;7). The aim of the research is to analyse the production of suffixed and prefixed nouns, verbs, and adjectives in CS and CDS during the early stages of the acquisition of Lithuanian morphology. The acquisition of the Lithuanian derivational system seems to be quite an effortless process. Although a considerable number of errors occurred at the initial stages, the first derivational families emerged already at the age of 1;8–1;9, and the number of errors started to decrease rapidly. The period during which the first derivatives emerge in child speech corresponds to the transition from a premorphological to a protomorphological stage. Keywords: Lithuanian derivational morphology, verb, noun, prefix, suffix. [From the publication]