Ovarian carcinoma is the most lethal gynaecologic malignancy. Despite wide initial sensibility to chemotherapy especially to platinum-based regimens, the vast majority of patients with advanced stages of the disease develop recurrences and subsequent resistance to treatments. Ovarian cancer is actually considered as a heterogeneous disease at the clinical, histological and molecular level. In this review, the mechanisms of intrinsic sensitivity or resistance to treatment, especially to platinum-based chemotherapy are considered with particular reference to the significance of tumour heterogeneity. The molecular features involved in acquired resistance are reviewed and the current hypotheses are discussed. In particular, potential disruptions of the DNA reparation pathways are highlighted.