The purpose of this research was to trace the developmental steps in the acquisition of aspectual oppositions in Russian and to examine the validity of the 'aspect before tense' hypothesis for L1-speaking children. Imperfective/perfective verbs and their inflections, as well as aspectual pairs, were analysed in the first five months of verb production (and the respective months in the input) in three children. Additionally, the first four months of verb production were investigated in one boy with less data. Verb forms marked for the past and for the present occur simultaneously in all children. These early forms relate to 'here and now' situations: verbs marked for the past denote 'resultative' events that are perceived by the children as occurring during the speech time or immediately before it, while verbs marked for the present typically denote on-going events. Thus, with early tense oppositions (or tense morphology) children mark aspectual contrasts in the moment of speech: evidence in favour of the 'aspect before tense' hypothesis.
 
 A strong preference in using the perfective aspect for the past and the imperfective aspect for the present events has been found in both adults and children. Further, only very few aspectual pairs were documented within the analysed period (from the onset of verb production to the period when children produce rule-driven inflectional forms). The productive use of the finite forms of perfective and imperfective verbs doesn't concord with the ability of the productive use of the contrastive forms of one lemma. Data suggest that children (start to) learn aspectual forms in an item-based manner. The acquisition of aspectual oppositions (aspectual pairs) is lexically dependent and is guided by the contextual 'thesaurus'. Aspectual pairs are learned in a peace-meal way during much longer, than observed for this article, period of time. Generally, aspect is not learned as a rule, also because there are no (uniform) rules of forming of aspectual pairs, but as the 'satellite' of the inherent lexical meaning of verbs of diverse Aktionsarten.
 
 The issues addressed here are relevant for other Slavic languages, exhibiting the morphological category of aspect.