Background/Aim: Ovarian cancer (OVCA) is characterized by genomic/molecular intra-patient heterogeneity (IPH). Tissue histology and morphological features are surrogates of the underlying genomic/molecular contexture. We assessed the morphological IPH of OVCA tumor compartments and of lymphocytic infiltrates in multiple matched samples per patient. Materials and Methods: We examined 294 hematoxylin & eosin (H&E) OVCA tumor whole sections from 70 treatmentnaïve patients who had undergone cytoreductive surgery. We assessed morphological subtypes as immunoreactive (IR), solid-proliferative (SD), papilloglandular (PG), and mesenchymal transition (MT); subtype load per patient; stromal tumorinfiltrating lymphocyte (sTIL) density as average per sample; and, as maximal sTIL values (max-TILs) among all samples per patient, ovaries and implants. Results: Among all 294 tumor sections, the most frequent primary morphological subtype was PG (n=150, 51.0%), followed by MT (71, 24.1%), SD (48, 16.3%) and IR (15, 5.1%). Subtype combinations were observed in 67/294 sections (22.8%) and IPH in 48/70 patients (68.6%). PG prevailed in ovaries (p<0.001), SD and MT in implants (p=0.023 and p<0.001, respectively). sTILs were higher in SD compared to non-SD (p=0.019) and lower in PG, respectively (p<0.001). sTIL density was higher in implants than in ovaries (p<0.001). Higher max-TILs were associated with stage IV disease (p=0.043), upper abdominal dissemination (p=0.024), endometrioid histology (p=0.013), and grade 3 tumors (p=0.021). Favorable prognosticators were higher max-TILs per patient (PFS, OS) and higher SD-load (PFS). Conclusion: Clinically relevant morphological and host immune-response IPH appear to be the norm in OVCA. This may complicate efforts to decipher sensitivity of the tumor to certain treatment modalities from a single pre-operative biopsy. Pathologic diagnosis of epithelial ovarian cancer (OVCA) takes into account the different origin, pathogenesis and prognosis of major histologic types with minimal or no consideration of the biological characteristics of the tumors (1, 2). OVCA histological types are considered for patient management, while genetic counselling and tumor genotyping with particular emphasis on BRCA1/2, homologous recombination and mismatch repair deficiency were only recently recommended for maintenance treatment options (3, 4). OVCA is not among the first 10 causes of cancer-related morbidity but it ranks fifth with respect to cancer-related mortality (5, 6), necessitating improvement at all steps of patient management and a deeper understanding of tumor biology.