The purpose of this study is to examine the challenges faced by adults completing Swedish secondary school who are learning English and Swedish as second language simultaneously. The study was carried out among teachers and pupils in adult secondary education in central Sweden. Three sets of data were used: the grades of those who had studied both English and Swedish as a second language, a student questionnaire and semi-structured interviews of five English teachers in adult education. The data was analysed using a qualitative method and from the theoretical standpoint that languages demand both time and energy which results in a competition occurring between the languages (Csizér & Dörnyei 2005; Herdina & Jessner 2000). The results indicate that motivation is the key factor affecting language acquisition, while other factors include learning technique, educational background, and proficiency in L1 and L2.