As a result of its expanding evidence base from randomized controlled trials, cognitive therapy is becoming increasingly widely practised in the treatment of many mental health problems. However, little is known about the extent to which it is carried out competently in practice, nor about what characteristics of therapists may be associated with competence. In therapists claiming to practice cognitive therapy, this study examined the relationship of a number of therapist factors, including training, profession, experience, supervision and accreditation, to competence. Therapists (n = 24) taped a mid-treatment cognitive therapy session. An independent rater, blind to information about the therapist, assessed the competence shown by the therapist during this session using the Cognitive Therapy Scale (CTS). Five randomly selected tapes were rated by a second rater and the inter-rater correlations were high. Although all therapists had received some cognitive therapy training during basic professional qualification, therapists with formal post-qualification training in cognitive therapy showed significantly higher levels of competence than those without. Psychologists were rated as more competent than therapists from other professions on one of the CTS subscales (Interpersonal Effectiveness). Number of years of experience, frequency of supervision, and accreditation were unrelated to ratings of competence. A number of accredited cognitive therapists scored well below a widely used criterion of competence.