This is the first report of an early association between elevated fibrinogen and asymptomatic unicentric Castleman's disease (CD). A 49-year-old asymptomatic female who was serving as a normal control in an unrelated study was incidentally found to have significantly elevated levels of plasma fibrinogen. Upon further investigation with computer tomography scans and magnetic resonance imaging, the woman was found to have a mobile mass in the abdominal region which was surgically removed. Based on histological analysis, a diagnosis of CD was made. At four-month follow-up, no additional signs of CD were present and fibrinogen levels returned to the normal range. This report, therefore, signifies the importance for physicians to consider unicentric CD in the differential diagnosis when patients present with elevated levels of plasma fibrinogen. Awareness of this diagnostic possibility may lead to increased early diagnosis of CD before symptoms become apparent, and provide a marker candidate for CD activity that may assist in monitoring treatment success. [J Clin Exp Hematop 54(1): 85-88, 2014]