BACKGROUND: Risk factors for local recurrence after mastectomy in ductal carcinoma in situ (DCIS) emerged as a grey area during the second "Assisi Think Tank Meeting" (ATTM) on Breast Cancer. AIM: To review practice patterns of post-mastectomy radiation therapy (PMRT) in DCIS, identify risk factors for recurrence and select suitable candidates for PMRT. METHODS: A questionnaire concerning DCIS management, focusing on PMRT, was distributed online via SurveyMonkey. RESULTS: 142 responses were received from 15 countries. The majority worked in academic institutions, had 5-20 years work-experience and irradiated <5 DCIS patients/year. PMRT was more given if: surgical margins <1 mm, high-grade, multicentricity, young age, tumour size >5 cm, skin- or nipple- sparing mastectomy. Moderate hypofractionation was the most common schedule, except after immediate breast reconstruction (57% conventional fractionation). CONCLUSIONS: The present survey highlighted risk factors for PMRT administration, which should be further evaluated.