Immediate Breast Reconstruction (IBR) following mastectomy is an increasingly popular technique for the management of breast cancer. Recent literature has suggested that, among women who receive postmastectomy radiotherapy, IBR can prolong the time to the start of radiation relative to unreconstructed women. Importantly, thresholds were also discovered after which further delay of radiation is expected impact survival. Among IBR patients, the impact of mastectomy and reconstruction technique on time to initiation of radiotherapy has remained unexplored. We queried the National Cancer Database from 2004 to 2016 for women 18 years and older diagnosed with nonmetastatic breast cancer who underwent mastectomy, IBR and postmastectomy radiation. Mastectomy techniques included subcutaneous (i.e., skin sparing), simple, modified radical, or radical. IBR types were classified as either tissue-based (autologous), implant, combination, or other. Unreconstructed mastectomy patients who received postmastectomy radiation were included as a comparison group. Our outcome was calculated as the number of days from definitive surgery to the start of radiation. We used Analysis of Variance (ANOVA) to consider differences in this time interval by surgical technique. Ordinary least squares (OLS) regression was used to adjust for age, race, comorbidity, hospital readmission after surgery, stage, and diagnosis year. Results were considered separately for women receiving adjuvant, neoadjuvant or no chemotherapy. We identified 173,845 women diagnosed with breast cancer who received both mastectomy and postmastectomy radiotherapy. 47,575 (27%) of these women underwent IBR. The most popular reconstruction technique was implant-based. Regardless of chemotherapy, women receiving tissue-based reconstructions had the longest interval between surgery and radiation. This difference was pronounced among women who received no chemotherapy, with a delay of 116 days compared to 86 days among unreconstructed women (p = 0.027). On multivariable analysis, tissue-based reconstruction was associated with a 36-day increase in delay of radiation compared to unreconstructed patients (p<0.001). Overall, the delay from surgery to radiation decreased 16% from 2006 to 2015 in all postmastectomy cohorts (p<0.001). Hospital readmission within 30 days of surgery was an independent factor increasing the delay of radiation for women receiving adjuvant (18 days, p<0.001) and neoadjuvant chemotherapy (5 days, p = 0.027). This study supports the association between receipt of IBR and increased delay from surgery to initiation of radiotherapy. This was pronounced among women who received tissue-based reconstruction. While there has been a trend toward shorter delays between surgery and radiation over recent years in IBR patients, those receiving tissue-based reconstruction may be at higher risk for poor outcomes associated with delays.