BACKGROUND: Little is known about the differences in postoperative shoulder function following two common approaches for immediate breast reconstruction (IBR): abdominal-based breast reconstruction and implant-based breast reconstruction (ABR and IMBR). It was hypothesized that postoperative upper limb function would differ between the ABR and IMBR due to incomplete detachment of the pectoral muscles. PURPOSE: This study aimed to investigate the factors for shoulder function recovery post-IBR and compare recovery outcomes between ABR and IMBR. METHODS: This single-center prospective follow-up study included 60 patients who underwent IBR for 4 months postoperatively. Patients were invited to complete functional measurements 1 and 4 months postoperatively. The primary outcome was improvement in upper limb disability based on the Q-DASH score. Secondary outcomes were functional shoulder recovery markers: shoulder flexibility, strength, movement accuracy, scapular alignment, body schema accuracy, and neuropathic pain. Repeated-measures analyzes of variance and linear regression were performed. RESULTS: Within-group differences were found for most variables ( CONCLUSION: Postoperative shoulder function was comparable between the two IBR approaches. However, different factors were associated with improved upper limb disability between ABR and IMBR. Acute rehabilitation focused on resolving muscle tightness and pain may help mitigate upper limb disabilities following IBR.Trial registration number: KCT 0006501.