This research investigated the relations among clients' keeping relevant secrets in therapy, the working alliance, and symptom change. Clients (N = 83) in outpatient therapy and their therapists (N = 22) at a mental health hospital completed confidential surveys after a session of ongoing therapy. The clients who reported keeping a relevant secret (27.7%) scored significantly lower on the Working Alliance Inventory (WAI) than did clients who said that they were not, even when the analyses controlled for clients' social desirability scores and for therapist effects. Therapists of these clients also reported a weaker working alliance, even though the therapists typically did not know that the clients were keeping a relevant secret. However, keeping a relevant secret was not related to symptom change. The findings support the long-standing belief that secret keeping in therapy either hurts the therapeutic relationship or happens when the relationship is relatively weak.