Therapeutic alliance is an important element of evidence-based treatments for people diagnosed with a serious mental illness. Cognitive enhancement therapy (CET) is an efficacious cognitive rehabilitation programme that emphasizes coach-participant relationships. The purpose of this study was to examine experiences of therapeutic alliance among CET participants.We used an exploratory qualitative approach.Semi-structured interviews were conducted with 24 participants diagnosed with a serious mental illness. Interview transcripts were analysed by three independent coders using thematic analysis.Four themes related to therapeutic alliance emerged: (1) positive regard; (2) collaboration; (3) authenticity; (4) negative alliance.Findings suggest that therapeutic alliance is an important component of CET that bolsters the learning environment and ensures a positive group experience. Our qualitative analyses contribute greater understanding of how strong therapeutic relationships impact people with serious mental illnesses participating in evidence-based treatments beyond psychotherapy context.