Purpose Immediate breast reconstruction (IBR) at the time of mastectomy is gaining popularity, as studies show no negative impact on recurrence or patient survival, but better aesthetic outcome, less psychological distress and lower treatment costs. Using the largest database available in Europe, the presented study compared outcomes and complications of IBR vs. delayed breast reconstruction (DBR). Methods 3926 female patients underwent 4577 free DIEP-flap breast reconstructions after malignancies in 22 different German breast cancer centers. The cases were divided into two groups according to the time of reconstruction: an IBR and a DBR group. Surgical complications were accounted for and the groups were then compared. Results Overall, the rate of partial-(1.0 versus 1.2 percent of cases; p = 0.706) and total flap loss (2.3 versus 1.9 percent of cases; p = 0.516) showed no significant difference between the groups. The rate of revision surgery was slightly, but significantly lower in the IBR group (7.7 versus 9.8 percent; p = 0.039). Postoperative mobilization was commenced significantly earlier in the IBR group (mobilization on postoperative day 1: 82.1 versus 68.7 percent; p