Internet-based cognitive behaviour therapy (ICBT) is efficacious for treating depression, with therapist guidance identified as important for favourable outcomes. We have limited knowledge, however, about the fundamental components of therapist guidance in ICBT. The purpose of this study was to systematically examine therapist messages sent to patients during the course of ICBT for depressive symptoms in order to identify common “therapist behaviours” and the extent to which these behaviours correlate with completion of modules and improvements in symptoms at post-treatment, one- and two-year follow-up. A total of 664 e-mails from 5 therapists to 42 patients were analysed using qualitative content analysis. The most frequent behaviour was encouraging that accounted for 31.5% of the total number of coded behaviours. This was followed by affirming (25.1%), guiding (22.2%) and urging (9.8%). Less frequently the therapists clarified the internet treatment framework, informed about module content, emphasised the importance of patient responsibility, confronted the patient and made self-disclosures. Six of the nine identified therapist behaviours correlated with module completion. Three behaviours correlated with symptom improvement. Affirmingcorrelated significantly (r = .42, p = .005) with improvement in depressive symptoms at post-treatment and after two years (r = .39, p = .014). Encouraging was associated with outcome directly after treatment (r = .52, p = .001). Self-disclosure was correlated with improvement in depressive symptoms at post-treatment (r = .44, p = .003). The study contributes to a better understanding of therapist behaviours in ICBT for depressive symptoms. Future directions for research are discussed.