Objective: Several studies propose that patient attachment to therapist is associated with therapy outcome. However, the magnitude of the effect is diverse, which might be explicable by suppressor effects and the new concept of pseudo‐security. Method: Associations between patient attachment to therapist (client‐attachment‐to‐therapist‐scale [CATS]) and psychotherapy outcome ("global severity index" of the Symptom Check List) were evaluated in N = 368 patients. Multilevel models were performed. Results: When tested in separate models, secure attachment to therapist was associated with a more favourable outcome (p < 0.05), whereas avoidant and preoccupied attachment to therapist were correlated with a less favourable outcome (both p < 0.05). Avoidant but not preoccupied attachment to therapist suppressed the association between secure attachment to therapist and the outcome. When controlling for the other two CATS scales, avoidant as well as preoccupied attachment to therapist remained associated with a less favourable outcome (p < 0.05). Conclusion: Avoidant attachment to therapist suppresses the association between secure attachment to therapist and psychotherapy outcome. Pseudo‐security has to be taken into consideration in self‐report data on patient attachment to therapist.