The objective of this study was to analyze the expression and clinical role of the high mobility group AT hook (HMGA) protein in advanced-stage serous ovarian carcinoma. HMGA2 protein expression was investigated in 199 effusions and in 50 patient-matched primary tumors and solid metastases using immunohistochemistry. Results were analyzed for association with clinicopathologic parameters, including chemotherapy response, and survival. HMGA2 was expressed in tumor cells in 94.5 %, 96 %, and 90 % of specimens, respectively. There was no difference in HMGA2 expression between patient-matched samples from different anatomic sites (p > 0.3). HMGA2 expression in chemo-naïve samples was significantly higher in older patients (p = 0.006, p = 0.01, and p = 0.005 for effusions, primary tumors, and solid metastases, respectively). No association was found with residual disease volume. Furthermore, HMGA2 expression was not associated with FIGO stage (p > 0.2), except in chemo-naïve effusions (n = 106, p = 0.016). There was no difference in HMGA2 expression between chemo-naïve samples and samples obtained post-chemotherapy in effusions (p = 0.2) or primary tumors (p = 0.1). However, solid metastases obtained after chemotherapy exposure had higher HMGA2 expression compared with chemo-naïve samples (p = 0.032). HMGA2 expression was unrelated to chemotherapy response or survival. However, it was directly related to protein expression of the previously studied cancer stem cell marker Nestin (p = 0.01) and the gap junction protein claudin-7 (p = 0.02) and inversely related to the mRNA level of the E-cadherin repressor SIP1 (p = 0.02). This study provides evidence that HMGA2 is universally expressed in advanced-stage ovarian serous carcinoma irrespective of anatomic site, suggesting that HMGA2 may have a clinical role as therapeutic target.