Narcissism can be seen along a continuum of adjustment with well-defended narcissism on the adjusted end, and poorly-defended narcissism on the maladjusted end. Poorly-defended narcissism is associated with negative emotions, and somatic preoccupations. The present study investigated whether aspects of poorly-defended narcissism can be changed during hospital treatment and if the change predicts therapy outcome. Data from 1442 psychosomatic in-patients (70% women, mean age 40.1 years) at admission and discharge were analyzed. Narcissism, mood and quality of life were assessed with standardized instruments. Patients with somatoform, anxiety, depressive or adjustment disorders differed significantly in narcissistic aspects. During inpatient treatment, narcissistic aspects decreased, and mood and quality of life increased. Changes in threatened self were associated with an improvement on all mood dimensions. Psychosomatic hospital treatment can help patients with poorly-defended narcissism to regulate aspects of threatened self with subsequent positive impact on mood and quality of life.