Purpose: Recent reports from the IMS 3 trial showed the importance of early reperfusion to functional recovery after mechanical thrombectomy. The purpose of this study was to determine the cause(s) for delaying the start of IA intervention in the Penumbra trials. Methods: A pooled analysis of 1028 patients was conducted in the prospective (Pivotal N=124, PICS N=261, START N=133) and retrospective/registry (POST N=108, RetroSTART N=191, Speed 054 N=71) Penumbra trials. All obtained treatment at <8 hours from stroke symptom onset. Tested covariates (patient demographics, admission NIHSS scores, time of presentation from onset, day of the week presented to the hospital, IV tPA, and pre-treatment infarct size) were considered in the multivariable model. Results: Among the patients reviewed, 888 met study criteria. Mean age was 66.1±15.0 and 52.3% were female (464/888). Average NIHSS at admission was 17.5 ± 6.2 and 46.0% were administered IV-tPA prior to mechanical thrombectomy. Mean pre-treatment ASPECTS score was 7.5± 2.1. The average time from symptom onset to hospital presentation was 129.1±100.7 minutes and the average time from presentation to procedure start was 134.9±75.2 minutes. There is a significant, inverse relationship between onset to hospital and onset to groin puncture (R=-0.350, p<0.0001). Patients who presented late to the hospital were often treated earlier. Similarly, patients who experienced delays prior to arrival at the hospital were more likely to have a larger infarct core as indicated by a significantly lower ASPECTS score (p=0.028). In a multivariate analysis, a shorter symptom onset to presentation significantly predicts in-hospital delays (p<0.0001). Admission NIHSS scores, target vessel location, day of the week presentation, or IV lytic treatment were not significant contributing factors to the delay in endovascular treatment. Conclusion: In this pooled cohort of Penumbra cases, delay to IA therapy was predicted by an early presentation to the hospital and a smaller infarct core. Our findings suggest that there is a need to conduct an intensive review of in-hospital triaging procedures for endovascular therapy.