BACKGROUND: Women who have a mastectomy for breast cancer treatment or risk reduction may be offered different options for breast reconstruction, including use of implants or the woman's own tissue (autologous tissue flaps). The choice of technique depends on factors such as the woman's preferences, breast characteristics, preoperative imaging, comorbidities, smoking habits, prior chest or breast irradiation, and planned adjuvant therapies. OBJECTIVES: To assess the effects of implants versus autologous tissue flaps for postmastectomy breast reconstruction on women's quality of life, satisfaction, and short- and long-term surgical complications. SEARCH METHODS: We searched the Cochrane Breast Cancer Group's Specialised Register, CENTRAL, MEDLINE, Embase, and two trials registries in July 2022. SELECTION CRITERIA: We included studies that compared implant-based reconstruction with autologous tissue-based reconstruction following mastectomy for breast cancer treatment or risk reduction. The minimum eligible sample size was 100 participants. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed risk of bias and extracted data using standard Cochrane procedures. We used GRADE to assess the certainty of the evidence. MAIN RESULTS: Thirty-five non-randomised studies with 57,555 participants met our inclusion criteria. There were nine prospective cohort studies and 26 retrospective cohort studies. We judged 26 studies at serious overall risk of bias and the remaining studies at moderate overall risk of bias. Some studies measured quality of life and satisfaction using the BREAST-Q (scale of 0 to 100, higher is better). Implants may reduce postoperative psychosocial well-being compared with autologous tissue flaps (mean difference (MD) -4.26 points, 95% confidence interval (CI) -4.91 to -3.61; I² = 0%; 6 studies, 3335 participants; low-certainty evidence). Implants may reduce or have little to no effect on postoperative physical well-being compared with autologous tissue flaps, but the evidence is very uncertain (MD -1.92 points, 95% CI -4.44 to 0.60; I² = 87%; 6 studies, 3335 participants; very low-certainty evidence). Implants may reduce postoperative sexual well-being compared with autologous reconstruction (MD -6.63 points, 95% CI -7.55 to -5.72; I² = 0; 6 studies, 3335 participants; low-certainty evidence). Women who undergo breast reconstruction with implants versus autologous tissue flaps may be less satisfied with the breast, but the evidence is very uncertain (MD -8.17 points, 95% CI -11.41 to -4.92; I² = 90%; 6 studies, 3335 participants; very low-certainty evidence). This outcome refers to a woman's satisfaction with breast size, bra fit, appearance in the mirror (clothed or unclothed), and how the breast feels to touch. Women who undergo breast reconstruction with implants versus autologous tissue flaps may be less satisfied with the reconstruction (MD -5.96 points, 95% CI -10.24 to -1.68; I² = 62%; 4 studies, 1196 participants; low-certainty evidence). This outcome refers to whether the aesthetic outcome has met the woman's expectations, the impact surgery has had on her life, and whether she thinks she made the right decision to have the reconstruction. Implants may reduce or have little to no effect on the risk of short-term complications compared with autologous tissue flaps, but the evidence is very uncertain (risk ratio (RR) 0.80, 95% CI 0.63 to 1.03; I² = 91%; 22 studies, 34,244 participants; very low-certainty evidence). Implants may increase long-term complications compared with autologous tissue flaps, but the evidence is very uncertain (RR 1.56, 95% CI 1.09 to 2.22; I² = 94%; 17 studies, 26,930 participants; very low-certainty evidence). Implants may have little to no effect on the need for reintervention compared with autologous tissue flaps, but the evidence is very uncertain (RR 1.23, 95% CI 0.91 to 1.68; I² = 93%; 15 studies, 14,171 participants; very low-certainty evidence). Implants may reduce the duration of surgery compared with autologous tissue flaps, but the evidence is very uncertain (MD -125.04 minutes, 95% CI -131.41 to -118.67; I² = 0; 2 studies, 836 participants; very low-certainty evidence). AUTHORS' CONCLUSIONS: The findings of this review show that autologous tissue-based reconstruction compared with implant-based reconstruction may improve participant-reported outcomes such as psychosocial well-being, sexual well-being, and satisfaction with the reconstruction. There is also very uncertain evidence to suggest that autologous tissue-based reconstruction increases satisfaction with the breast and reduces the risk of long-term complications compared with implants. Implant-based reconstruction may be a shorter procedure, but the evidence is very uncertain. Despite the growing demand for breast reconstruction, the best technique has not been adequately studied in randomised controlled trials (RCTs), and the evidence provided by non-randomised studies is often unsatisfactory. There is no superior breast reconstruction technique for all women. Future research should focus on the definition of decisional drivers to guide an evidence-based shared decision-making process in reconstructive breast surgery.