Immigration in recent decades has configured a more multilingual space than there has ever been before in Spain. The double purpose of this study was to discover self-reported use of language by foreigners and their linguistic competence in both formal and informal Spanish environments. An Index of Linguistic Competence in Spanish (ILCS) based on oral, phonetic, written and comprehension capabilities was designed for this. Data were from a survey given to the foreign population aged 14 to 18 residing in the Province of Almeria (Spain). The results show that the level they have acquired is lower than native students. Furthermore, there are considerable differences among the foreigners themselves by age, years of residence in Spain, years in school, and origin.