Background/Objectives: Breast cancer is the most common cancer among women worldwide. Surgical treatments include breast-conserving therapy (BCT) and mastectomy, often followed by reconstruction, but the impact of reconstruction on locoregional recurrence (LRR) remains unclear. This study evaluated LRR, survival, and risk factors following primary breast reconstruction performed simultaneously with mastectomy compared with mastectomy without reconstruction. Methods: This population-based, retrospective cohort included 2475 women with breast cancer treated between 2004 and 2018 at the Tumor Center and Caritas St. Josef Hospital in Regensburg, Germany. Patients were grouped into not primarily reconstructed, primary autologous reconstruction, primary allogeneic reconstruction, and primary combined reconstruction. Overall survival (OS), recurrence-free survival (RFS), and cumulative recurrence rates (CRR) were assessed using Kaplan–Meier methods and Cox proportional hazards models adjusted for age, nodal status, tumor biology, and adjuvant therapies. Results: Of 14,046 eligible cases, 2475 met inclusion criteria: no primary reconstruction (87%), autologous reconstruction (3.1%), allogeneic reconstruction (9.0%), and combined reconstruction (0.4%). Patients undergoing reconstruction were younger and more likely to receive chemotherapy. The 5-year OS was 71.8% without primary reconstruction, 82.1% after autologous reconstruction, and 90.0% after allogeneic reconstruction. Allogeneic reconstruction was associated with improved OS (HR 0.570, p = 0.015) and RFS (HR 0.669, p = 0.039), whereas autologous reconstruction was associated with higher hazards of LRR and distant metastases compared to no primary reconstruction. Conclusions: The 5-year cumulative LRR was 5.2%, 13.5%, and 4.8%, respectively. Immediate allogeneic reconstruction after mastectomy was therefore associated with favorable survival and recurrence outcomes, while autologous reconstruction was linked to higher LRR and distant metastasis rates in this cohort. The retrospective design, small autologous subgroup, and absence of detailed lifestyle and metabolic data are important limitations of these findings. These associations likely reflect differences in tumor stage, biology, and unmeasured risk factors, and should be interpreted as hypothesis generating. Prospective multicenter studies with detailed risk profiling are needed to clarify the oncologic safety of different reconstructive strategies.