Purpose: Breast conserving therapy (BCT) is the standard of care for early-stage breast cancer. Further re-excision surgery may be required if adequate surgical margins are not achieved. This study investigated the incidence of residual disease and prognostic factors in patients undergoing re-excision after breast conserving surgery (BCS) for invasive breast cancer and/or ductal carcinoma in-situ (DCIS). Methodology: A prospective database of all patients with invasive breast cancer and/or DCIS between 2018 – 2022 was used to identify patients. A retrospective review of electronic medical records of these patients undergoing BCS was performed where clinicopathologic factors predicting residual disease were investigated. Results: One-hundred and eighteen patients were divided into two categories: those with no residual disease (n = 68) and those with residual disease on re-excision surgery (n = 50). The overall incidence of residual disease was 42.4%. Patients receiving magnetic resonance imaging (MRI) breasts before re-excision surgery (OR: 3.76, P = 0.016) and those with larger tumour size (OR: 1.06, P = 0.014) were more likely to have residual disease. Patients receiving radiotherapy were less likely to have residual disease (OR: 0.21, P = 0.010). Conclusion: The incidence of residual disease on re-excision was 42.4% for our study cohort. Patients undergoing BCS for invasive breast cancer and/or DCIS with larger tumour size are more likely to have residual disease on re-excision surgery. Judicious use of MRI after a breast cancer multidisciplinary meeting (MDM) discussion can help identify patients likely to have residual disease and can help plan further re-excision surgery.