A growing body of evidence points to significant interpersonal problems associated with narcissism in clinical samples. Less well understood are the mechanisms by which narcissism negatively impacts one’s interpersonal functioning. The present study investigated defensive style as a possible mediator of the relationship between narcissism and interpersonal problems. A sample of 53 adult psychiatric outpatients completed measures of narcissism, defensive style, interpersonal problems, and current symptom distress. Mediation analysis was conducted, controlling for current symptom distress, using 95% bootstrapped confidence intervals to examine the indirect effect of narcissism on interpersonal problems via defensive style. Narcissism was significantly associated with immature and neurotic defensive styles. Although narcissism was not directly related to interpersonal problems, a significant indirect effect was observed for narcissism on interpersonal problems via neurotic defensive style. This finding suggests that narcissism contributes to the use of neurotic defenses, which in turn influence one’s interpersonal functioning.