Native Spanish speakers tend to show difficulties when pronouncing English phonemes (Alcaraz & Moody, 1984). Most of these difficulties are due to cross-linguistic influence, but there is also a debate on whether age is a crucial factor (Muñoz 2010; Bongaers, Planken & Schils 1995). The aim of my study is to explore the difficulty experienced by Spanish speakers in the acquisition of the pronunciation of English as a second language, attending to linguistic and extralinguistic factors. The methodology is two-fold. First, I will examine the difficulty in differentiating four sets of sounds: the vowel phonemes /ӕ/-/ʌ/ and /ɪ/-/iː/, and the consonant phonemes /s/-/z/ and /d/-/ð/. Second, I will compare the acquisition of the selected phonemes in speaking tasks versus listening tasks. The subjects in my study are 20 Spanish-native speakers with a mean age of 15.2 years-old and who have been studying English for 12 years. The students are in their fourth year of high school (A2 level), located in the urban city of Vigo (Spain). The data are based on four skill tasks (two listening, two speaking) and a biographical survey. The results suggest that most of the inaccuracies observed between the pairs of phonemes examined are due to the influence of the students’ first language. The position of the phoneme in the word also seems to have an effect on the students’ production and perception. Another conditioning factor seems to be the (little) time devoted to teaching pronunciation skills in the classroom. This leads me to the general conclusion that more pronunciation exercises are needed and that these are likely to yield better production and perception skills.