We investigated if delayed breast implant reconstruction after breast cancer impairs prognosis. Using data from the Danish Breast Cancer Cooperative Group register, we identified all women <70 years who underwent breast reconstruction with implants after mastectomy after invasive breast cancer during 1978 to 1992, on average 2.2 years (range, 3 days-9.4 years) after mastectomy. The reconstructed women were closely matched to breast cancer patients without reconstruction on age and calendar time of diagnosis, tumor size, regional lymph node involvement, and adjuvant radiation therapy. Overall, 580 reconstructed women and 1158 individually matched controls were followed-up for disease-free survival within the first 10 years and for overall survival for an average of 20.1 year (range, 12.8-27.5 years). Disease-free survival was significantly improved hazard ratio 0.78; 95% confidence interval 0.64-0.95 and overall survival was nonsignificantly improved (hazard ratio, 0.90; 95% confidence interval 0.76-1.06) among the breast reconstructed women. This is likely because of differences in socioeconomic and health factors.