The present study probed the effectiveness for L2 writing of Longman Słownik Współczesny ( Fisiak et al. 2004 ), a bilingual dictionary for Polish learners of English designed primarily with production tasks in mind ( Adamska-Sałaciak 2005 ). Three groups of Polish secondary school students in their final year were asked to write an argumentative essay: one group with the help of a paper copy of Longman Słownik Współczesny , one with a PC version of the dictionary, and one control group without access to a dictionary. The essays were marked using the standard rubric for Polish secondary school final examinations, with separate marks for content, structure, language, and accuracy. Results indicate that those students writing with the help of the dictionary (whether print or PC-based) performed significantly better than the controls without access to dictionaries, with overall scores gaining by about one third. The areas that benefitted most from dictionaries were vocabulary use and general accuracy. The results demonstrate that the dictionary is an effective writing aid for Polish learners of English.