This is a Phase 2, open-label, single arm study to evaluate the safety and efficacy of niraparib in ovarian cancer patients who have received at least three previous chemotherapy regimens. Niraparib is an orally active PARP inhibitor. Niraparib will be administered once daily continuously during a 28-day cycle. Health-related quality of life will be measured by Eastern Cooperative Oncology Group performance status (ECOG). Safety and tolerability will be assessed by clinical review of adverse events (AEs), physical examinations, electrocardiograms (ECGs), RECIST tumor assessments and safety laboratory values.