In this paper we present the principles of lexico-semantic annotation of Skadnica Treebank using Polish WordNet lexical units.We describe different means of annotation, depending on the structure of a sentence in Skadnica on the one hand and the availability of adequate lexical unit in PLWN on the other.Apart from "standard" annotation involving lexical units with the same lemma as the token under annotation, multi-word units, different verb lemmas including reflexive marker si as well as synonyms and hypernyms have also been involved.Some tokens have obtained tags explaining why they require no annotation.Additionally, we discuss the assessment of the annotation of whole sentences.