The occurrence of pathological narcissism in bipolar patients, and the diagnostic relation between narcissistic personality disorder (NPD) and bipolar disorder (BD), were investigated. The Diagnostic Interview for Narcissism (DIN) was administered to bipolar patients when manic and when euthymic. The scores were compared to those of an NPD sample and a control group of general psychiatric patients. Euthymic bipolars do not exhibit a higher level of pathological narcissism or a higher prevalence of NPD than psychiatric patients in general. However, when manic, bipolar patients do appear similar to the narcissistic group, sharing 12 out of 14 of the identifying criteria for NPD. The results support the inclusion of mania in the differential diagnosis of NPD.