In prosthesis-based breast reconstruction, drains are used to prevent seroma formation and to reduce the risk of infection. However, prolonged drainage increases the risk of ascending infection. Although the volume often accepted for drain removal is ≤30 mL per day, the optimal timing to remove the drain for best clinical outcome remains controversial.We did a retrospective cohort study of 569 patients of prosthesis-based breast reconstruction with infection rate as the outcome variable; drain duration and last daily drainage volume as the main independent variables. Data on age, smoking history, diabetes mellitus history, body mass index, breast weight, tissue expander size, drain size, number of retrieved lymph nodes, tumor size, number of metastatic lymph nodes, tumor stage, mastectomy type, reconstruction type, submuscular implantation, skin defect, operative time, duration of antibiotics use, chemotherapy, and radiotherapy were collected as covariates. Multivariable logistic regression analysis was used to control for confounding.The total infection rate was 5.1% (29/569). The daily drainage volume ≥30 mL/d at the time of drain removal was not found associated with increased infection rate (P = 0.32). Of the various cutoff values of last daily drainage volume, none was found to be a determinant for drain removal where the risk of infection was concerned. By contrast, drain duration over 21 days significantly increased infection rate (P = 0.001). The multivariable logistic regression analysis showed an increase of 76.2% in the infection rate with each additional week of drain retention (P = 0.001). Breast weight also had a significant influence on risk of infection. Chemotherapy and drain size showed borderline effect on risk of infection whereas the last daily drainage volume was not associated with risk of infectionIn summary, our study revealed that drain duration, rather than the last daily drainage volume, significantly affects the infection rate in prosthesis-based breast reconstruction. We recommend that the drain is better removed no longer than 3 weeks postoperatively and can be removed as early as postoperative day 7, even when the drainage is over 30 mL in a 24-hour period.