Background Sarcopenia, defined as a significant loss of skeletal muscle mass and function, is suggested to be associated with an increased risk of complications after various surgical interventions. However, evidence regarding sarcopenia in microsurgical breast reconstruction has been lacking. The present study was designed to evaluate the association between preoperative sarcopenia and adverse outcomes in deep inferior epigastric perforator (DIEP) flap-based breast reconstruction. Methods Patients who underwent breast reconstruction using DIEP flap between 2009 and 2018 were reviewed. Sarcopenia was defined as a skeletal muscle index < 38.5 cm 2 /m 2 , calculated by normalizing the cross-sectional area of the skeletal muscle, measured at the level of the third lumbar vertebra based on preoperative computed tomography angiography, to patient height. Postoperative complication rates were compared between patients with sarcopenia and those without it. Independent association of sarcopenia with complication profiles were evaluated. Further analyses were conducted using propensity score matching. Results In total, 557 patients were analyzed, of which 154 (27.6%) had preoperative sarcopenia. The sarcopenia group had a significantly lower body mass index, a lower elevated flap weight, and greater use of bipedicled flaps compared to the nonsarcopenia group. Complications developed in 128 patients (23.0%) and were more prevalent in the sarcopenia group. Preoperative sarcopenia was associated with a significantly higher rate of complications, including breast hematoma, breast wound problems, abdominal functional weakness, and reoperation in the multivariable analyses. Similar associations were observed in the propensity score matching analysis. Conclusions Preoperative sarcopenia appears to be associated with adverse outcomes in DIEP flap-based breast reconstruction.