Background: Poly (ADP-ribose) polymerases (PARPs) are a highly conserved family of enzymes whose main function is to preserve genomic integrity following DNA damage. PARP inhibitors (PARPi) are increasingly used in cancers with deficiencies in homologous recombination. Clinical trials in breast and ovarian cancers have led to several FDA approvals in recent years, and their use in clinical practice is continuing to rise. It is thus necessary to assess their adverse event (AE) profile. Method: Literature search was performed using Ovid MEDLINE, EMBASE, CENTRAL, and Scopus (inception through October 26, 2018). Eligible studies were phase 3, randomized, controlled trials that compared single agent PARPi to placebo or standard treatment. Number of patients treated and AEs reported were recorded. Observed incidence of AE was reported with 95% CI. Heterogeneity was evaluated using Cochran Q statistic and I2 statistics quantified the proportion of heterogeneity not due to chance. Results: Databases revealed 869 references. Of these, 6 were eligible: 2 in breast cancer (OlympiAD, EMBRACA) and 4 in ovarian cancer (NOVA, ARIEL3, SOLO1, SOLO2). PARPi included niraparib (NOVA), olaparib (OlympiAD, SOLO1, SOLO2), rucaparib (ARIEL3), and talazoparib (EMBRACA). Of 1,685 patients who received PARPi, incidence of any AE, regardless of grade, was 98.5% (95% CI, 97.2–99.2%). Common AEs were: nausea (incidence rate, 68.9% and 95% CI, 58.7%–77.5%), fatigue (56.3%, 45.3%–66.8%), anemia (46.3%, 37.2%–55.8%), vomiting (33.7%, 29.5%–38.3%), neutropenia (24.7%, 15.3%–37.4%), headache (23.9%, 19.9%–28.4%), and reduced appetite (21.7%, 19.3%–24.3%). Myeloid neoplasms were rare (1.2%, 0.7%–1.9%). Incidence of grade 3 or higher AE was 44.3% (30.2%–59.5%) and often related to myelosuppression, specifically anemia (24.7%, 15.3%–37.4%), neutropenia (10.7%, 6.6%–16.9%), and thrombocytopenia (5.0%, 1.7%–14.0%). Incidence of serious AE was 24.3% (19.4%–29.9%); dose interruption occurred in 53.3% (41.2%–65.0%) and dose reduction occurred in 39.2% (23.6%–57.4%). 10% (7.4%–13.6%) of patients discontinued therapy due to AE. Death due to AE was rare; less than 1% (0.4%, 0.2%–0.8%) in all trials. Conclusion: Myelosuppression and gastrointestinal toxicities were the most commonly reported AE in 6 randomized phase 3 trials of PARPi for breast and ovarian cancers. Therapy was rarely discontinued due to AE. It remains to be seen whether these results will be reflected in clinical practice.