OBJECTIVEIncidence rates of de novo aneurysm formation and recurrence after clip ligation remain controversial. In this meta-analysis, the authors provide data on pooled annual incidence rates and the association of patient characteristics with time to formation of de novo aneurysms and time to recurrence after clipping.METHODSA search of the literature up to June 15, 2016, on PubMed and a systematic review were performed. The association of age, aneurysm rupture status, aneurysm multiplicity, and anatomical location with time to recurrence or formation of de novo aneurysm was estimated using multivariable Cox proportional-hazards models. Kaplan-Meier estimates (event-free survival curves) are shown. Pooled annualized incidence rates of recurrent and de novo aneurysms were estimated using Poisson regression. Proportions of aneurysms and average follow-up times are displayed as bubble plots with LOESS smoothers weighted for study size.RESULTSOf the 7606 articles screened, 92 were included in the study. Case reports on 101 patients with recurrent aneurysms and 132 patients with de novo aneurysms were analyzed. Long-term follow-up studies on de novo aneurysm formation included 13,723 patients with 101,378 patient-years of follow-up; studies on aneurysm recurrence included 5922 patients with 31,055 patient-years of follow-up. Mean time to recurrence was 12.9 ± 6.6 years (mean ± standard deviation), and mean time to de novo formation was 9.3 ± 6.1 years. No association with sex, aneurysm location, and initial rupture could be shown. De novo aneurysms occurred later in patients with multiplicity of aneurysms at diagnosis (HR 0.63, p = 0.03) and in patients with increasing age (HR per 10 yrs 0.88, p = 0.06). Pooled annualized incidence rates were 0.35% for de novo aneurysms and 0.13% for recurrent aneurysms.CONCLUSIONSDespite low reported annual incidence rates, the cumulative risk of 9.6%–22% for aneurysm recurrence or de novo formation 20 years after clip ligation warrants lifelong follow-up. Screening at 5, 10, and 20 years would detect 30.8% (95% CI 23.3%–37.6%), 64.2% (95% CI 55.9%–70.9%), and 95.9% (95% CI 90.9%–97.9%) of de novo aneurysms. Screening for recurrent aneurysms at 10, 15, and 20 years would detect 36.6% (95% CI 26.5%–45.4%), 65.3% (95% CI 54.7%–73.5%), and 95.1% (95% CI 85.8%–96.6%) of lesions.