To evaluate psychological treatments for adolescent binge-eating disorder (BED), reliable information on therapeutic process factors is needed. This study examines therapist adherence and therapeutic alliance and their associations in cognitive-behavioural therapy (CBT) for adolescents with BED. In a randomised-controlled efficacy trial, adherence and alliance were objectively determined based on 247 audio-taped CBT sessions from a sample of N = 64 adolescents with BED. Variability of adherence and alliance, explained by treatment module, patient, and therapist were examined using multilevel modeling. Although adherence and alliance were excellent and unaffected by treatment module and therapist, there was significant between-patient variability for both concepts. Adherence was negatively associated with patient's treatment expectation. Alliance was negatively associated with the number of loss of control eating episodes and positively associated with adherence. Excellent adherence supported the internal validity of CBT for adolescent BED. Associations between process factors and patient characteristics demand adequate supervision in CBT.