This article analyses the acoustical properties of Dutch vowels produced by adult Spanish learners and investigates how these vowels are perceived by non-expert native Dutch listeners. Statistical vowel classifications obtained from the acoustical properties of the learner vowel realizations were compared to vowel classifications provided by native Dutch listeners. Both types of classifications were affected by the specific set of vowels included as stimuli, an effect caused by the large variability in Spanish learners’ vowel realizations. While there were matches between the two types of classifications, shifts were noted within and between production and perception, depending on the vowel and vowel features. We considered the variability between Spanish learners further by investigating individual patterns in the production and perception data, and linking these to the learners’ proficiency level and multilingual background. We conclude that integrating production and perception data provides valuable insights into the role of different features in adult L2 learning, and how their properties actively interact in the way L2 speech is perceived. A second conclusion is that adaptive mechanisms, signalled by boundary shifts and useful in coping with variability of non-native vowel stimuli, play a role in both statistical vowel classifications (production) and human vowel recognition (perception).