ObjectiveStudies indicate a significant challenge for therapists in forming a therapeutic alliance (TA) with patients coping with anorexia nervosa (AN). While TA is a significant predictor of treatment outcomes, and AN treatment has low success rates, little is known about factors that affect the formation of an alliance and its quality in the treatment of AN. This study aimed at examining the factors associated with alliance formation, as perceived by patient–therapist dyads throughout AN therapy.MethodsA total of 18 dyads of patients with AN and their therapists were recruited from an eating disorder unit. The semistructured interviews focussed on the TA between the therapist and patient and examined facilitators towards, and barriers to, TA formation. Data analysis followed a thematic approach.ResultsThe data analysis revealed an overarching theme: the mutual wish of the patient and therapist to form a close relationship and related challenges. This theme was divided into subthemes: (1) the role of self‐disclosure of affection; (2) the meaning of the therapeutic setting; (3) coping with relationship ruptures; and (4) the importance of empathic acknowledgements.ConclusionA major barrier to TA formation between patients with AN and their therapists is patients' conflict between a need for meaningful relationships and fear of re‐experiencing disappointment and pain. Self‐disclosures of affection, flexible treatment setting, acknowledgement of therapists' empathic failures and ability to see things from patients' perspectives are perceived by therapists and patients to facilitate alliance formation. This study also presents practical implications derived from these themes.