Ovarian cancer has a high mortality rate. Serous carcinoma is the most common subtype and can be detected by distant or lymph node metastasis in advanced stages. Apelin, an adipokine associated with obesity, and its receptor, APJ, participate in lymphatic invasion. Angiogenesis also can affect lymph node involvement in serous ovarian carcinomas. We investigated apelin/APJ receptor immunoreactivity in stages III and IV ovarian cancer with or without lymph node involvement and correlated the results with body mass index (BMI) to determine whether the potential relation of the two affects the outcome of the cancer. We investigated 30 patients diagnosed between 2014 and 2016 with high grade serous ovarian cancer. Tumor:stroma ratio, indirect immunoperoxidase method, H-score and MATLAB analysis were performed. In obese and pre-obese patients, tumor apelin immunoreactivity was stronger than for patients with normal BMI. Tumor:stroma ratio was correlated with survival and lymph node involvement. Strong apelin and moderate APJ immunoreactivity was detected in both lymph node negative and positive patients. BMI was related to both survival outcome and apelin immunoreactivity. BMI, adipokines such as apelin, and the stromal compartment play critical roles in advanced stage serous carcinomas.