The literature portrays patients with alexithymia as unusual and difficult to treat; research to date has not clarified the nature of this condition. This study addressed associations between alexithymia and constructs relevant to clinical intervention, namely attachment, quality of object relations, emotion regulation, defense style, personality disorder, and treatment outcome. Fifty-one patients admitted to an intensive group-oriented day treatment program were recruited. Prior to therapy, patients were administered self-report and structured interview measures of predictor and outcome variables; outcome measures were re-administered at completion of the 18-week program. Alexithymia was common in this sample, with four of five patients endorsing moderate or greater problems. Associations with attachment avoidance, primitive object relations, suppression of emotional expression, use of immature defenses, and severity of borderline personality disorder were identified. Alexithymia did not, however, predict outcome. Findings are considered in terms of how the construct informs views of personality disorder.