Active surveillance trials for low-risk ductal carcinoma in situ (DCIS) are in progress in the United States and Europe. In some of these trials, the presence of comedo necrosis in the DCIS has been an exclusion criterion for trial entry. However, the minimum amount of necrosis required by pathologists for a diagnosis of comedo necrosis is not well-defined. We surveyed 35 experienced breast pathologists to assess their diagnostic threshold for comedo necrosis. Pink circles representing necrosis ranging in extent from 10 to 80% of the duct diameter were superimposed on eight replicate histologic images of a single duct involved by low nuclear grade, solid pattern DCIS. These images were circulated by e-mail to the participating pathologists who were asked to select the image that represents the minimum amount of necrosis that they require for a diagnosis of comedo necrosis. Among the 35 participants, the minimum extent of the duct diameter required for a diagnosis of comedo necrosis was 10% for 4 pathologists, 20% for 5, 30% for 11, 40% for 7, 50% for 6, 60% for 1 and 70% for 1. There was no single threshold about which more than one-third of the pathologists agreed met the minimal criteria for comedo necrosis. We conclude that even among experienced breast pathologists, the threshold for comedo necrosis is highly variable. Our findings highlight the need for a standardized definition of comedo necrosis as a trial criterion, and more generally where it may be used as a marker of increased risk of recurrence for therapeutic decision making.