Positive tumour margins after breast-conserving surgery (BCS) have been selected as one of the major quality criteria for the surgical treatment of localized primary breast cancer. The national guideline states that the rate of positive margins should not exceed 30% in ductal carcinoma in situ and 20% in invasive cancers. We aimed to determine whether BCS in women with screen-detected breast cancer (SDBC) will have positive margins less often compared with women with clinically detected breast cancer (CDBC). Furthermore, the choice of subsequent therapy is studied when margins were positive after initial BCS. Women 50-75 years of age who underwent BCS for invasive breast cancer between July 2008 and December 2009 were selected from the Netherlands Cancer Registry. Data were merged with the National Cancer Screening Program, regions North and East, to identify women with SDBC. The relation to screening history, clinical and pathological factors was evaluated for correlation with margin status using multilevel analysis. Of 1537 women with an invasive breast cancer, 873 (57%) were diagnosed through the screening programme. SDBCs were significantly smaller (87 vs. 69% T1 tumours, i.e. ≤2 cm), more often well differentiated (33 vs. 26%), preoperatively confirmed (98 vs. 96%), diagnosed in a nonteaching hospital (60 vs. 66%) and more often had negative lymph nodes (LNs) (80 vs. 68%). In 170 out of 1537 women, the resection margins were positive. Multivariable analysis showed that hospital, tumour size, multifocality, positive LNs and absent preoperative confirmation were predictors of positive margins. No difference was found between women with SDBC and CDBC. Of women with positive margins, 90% underwent additional surgery. Women diagnosed with SDBC do not have a lower risk of having positive margins after BCS than women with CDBC. Although positive margins may occur in 11% of women with invasive tumours, well below the percentage recommended by the national guideline, the presence of encouraging factors by SDBC such as a smaller tumour size, unifocality, negative LNs and the presence of preoperative confirmation should not lead to performing a more sparing excision than is considered usual for comparable CDBC.