Purpose: Guide-wire localization (GWL) has been a standard technique for many years. Excision of nonpalpable malignant breast lesions with clear surgical margins reduces the risk of undergoing re-excision. The objective of the present study was to evaluate the efficacy of GWL biopsy for assessing surgical margins. Methods: This retrospective study concerned 53 patients who underwent GWL biopsy for non-palpable breast lesions and breast carcinoma diagnosed by histological examination. Age of the patients, tumour size, radiographic findings, breast density specifications, specimen volumes, menopausal status and family history of the patients and surgical margin status were recorded. Results: Median age was 53.3 years, median tumour size was 1.5 cm and median specimen volume was $71.5cm^3$. In fifteen patients (28%) DCIS and in 38 patients (72%) invasive ductal carcinoma was diagnosed. There was positive surgical margins in twenty eight (52.8%) patients. The median distance to the nearest surgical margin was 7.2 mm in clear surgical margins. Younger age and denser breast specifications were found as statistically significant factors for surgical margin status. Median age of the patients who had positive margins was 49.4 years where it was 56.9 years in the patients with negative margins (p=0.04). 79% of the patients with positive margins had type 3-4 pattern breast density according to BIRADS classification as compared to 48% in the patients who had negative margins (p=0.03). Some 38 patients who had positive or close surgical margins received re-excision (72%). Conclusion: Positive margin rates may be higher because of inherent biological differences and diffuse growth patterns in younger patients. There are also technical difficulties that are relevant to denser fibroglandular tissue in placing hooked wire. High re-excision rates must be taken into consideration while performing GWL biopsy in non-palpable breast lesions.