Humour is an ever-present part of affective communication, and theories abound about its proposed role within psychotherapy. However, little empirical research has been carried out, and what could be a major psychotherapeutic resource, remains essentially untested. This study utilised mixed methods (semi-structured interviews and survey), to examine clients’ experiences of humour within psychotherapy. The findings indicate humour may be a marker of therapeutic relationship health, evidenced by thematic data showing clients only bring in humour when safety and trust are present and when they feel a connection with their therapist. This finding was further strengthened by survey data, showing that clients who rated their humour as well-matched to their therapists’ or rated their therapists’ humour as helpful, were more likely to rate the relationship as good.