Abstract:The present study aims to investigate the attrition of Portuguese as a third or additional language (L3, L4, etc., cf. de Angelis, 2007) over the summer holidays. The research questions concern the correctness of the participants' responses, the language areas in which attrition is observed, the ways in which it manifests itself and the students' perception of their own attrition. Since multilingual systems are dynamic and the languages are in constant interaction, when a language is not used, attrition sets in (Herdina & Jessner, 2002). However, some elements of linguistic knowledge are more prone to attrition than others (SharwoodSmith, 1989). The study was carried out with 42 Polish (L1) learners of Portuguese, 30 of whom were second-year students of Portuguese philology, and 12 were students of other Romance philologies who followed a Portuguese language course. After the summer holidays, they completed a vocabulary and grammar test and participated in oral interviews, followed by a questionnaire. In general, they produced more incorrect and partly correct (e.g. the right verb in the wrong form) than correct responses. Attrition could be observed in various language areas, from speaking fluency to grammar and vocabulary, though the subjunctive, which they had only started to study before the holidays, caused them the most difficulty. The attrition of Portuguese manifested itself in various forms, from avoidance and the inability to retrieve certain items, through the confusion of Portuguese forms, to interference from other languages. As the questionnaire indicates, the students were aware of the areas in which attrition occurred. It can be concluded that attrition is connected mainly with a decrease in the activation of a language. Given the interference from other Romance languages, it can be supposed that, as the activation of Portuguese items is lower, Spanish, French and Italian items compete for selection.