The subject matter of the article is the substantive prerequisite for conditional release from serving the full sentence. The analysis of literature and case law makes it possible to state that the quantifiers laid down in Article 77 §1 CC, which a court should take into account when developing a prognosis concerning a convict’s conduct after the release from prison, give rise to difficulties connected with their identification. As a result, in their justification for refusal to grant conditional release courts often indicate criteria which are not laid down in Article 77 §1 CC. However, it seems purposeful to give up taking into account circumstances considered by a court when issuing the sentence because of their static nature.