Pienemann’s Processability Theory (PT) hypothesizes that the grammatical structures of a second language are acquired in an order that is universal for all languages. The main aim of this article is to investigate the validity and reliability of this theory for the acquisition process of Dutch as L2 by Polish students. PT was tested on a group of 15 first-year Dutch philology students at the University of Wrocław, after 300 hours of intensive Dutch language course. The oral production test checked the acquisition level of three Dutch grammatical structures, representing consecutive stages of L2-development: agreement between adjective and noun (stage III), agreement between verb and subject (stage IV) and word order in subordinate clauses (stage V). Pienemann’s hypothesis seems to be valid for the acquisition of Dutch language as L2 only if the criterion of one correct use of a grammatical structure is taken into consideration. When it comes to the two other criteria (50% and 90% of correct use) the structure representing stage III seems to be acquired after the structures representing stages IV and V, which forms a counter-evidence for the Processability Theory.