This paper presents a single case study investigating the use of cognitive behavioural therapy (CBT) with an adolescent experiencing a psychotic episode. The participant was a 15-year-old girl with first episode psychosis, who was an inpatient in an adolescent psychiatric unit. Progress was evaluated using an AB time series design, lasting 16 weeks in total. After a baseline assessment (A) the participant received a 16-week CBT intervention for psychosis (B). The effectiveness of the intervention was investigated with relation to psychotic symptoms, self-esteem, recovery style, person evaluations, anxiety and depression. The results indicated that there were some improvements in symptoms of anxiety, depression and psychosis but were inconclusive for the other measures. It is argued that the maintenance of negative person evaluations had a detrimental effect on the participant's ability to increase self-esteem, change recovery style and further reduce psychotic symptoms, anxiety and depression. The impact of environmental factors on the progression of the participant's illness is considered and the findings are discussed in relation to previous literature.