Historically, two major strata of ductal carcinoma in situ (DCIS) have been linked to outcome, the presence or absence of comedo type and size. Our initial approach in classification was dichotomous, often favoring the comedo type with most worrisome implications to foster agreement in diagnosis. We have now tested guidelines that foster agreement in the modified Lagios three-tiered system. Sixteen cases of DCIS were selected, reflecting a spectrum of histological subtypes, with specific inclusion of cases in which consensus in classification using a dichotomous (comedo/noncomedo) scheme would be difficult. Six independent observers reviewed a minimum of five color 35-mm slides from each case at two separate occasions. The aim was to subclassify each case based on architectural pattern, nuclear grade, and presence or absence of tumor necrosis (Modified Lagios Classification, Lagios et al, Cancer 1989). After initial review, emphasizing placement of each case into a high- or low-grade category, there was disagreement in seven cases (44%), confirming our aim to choose cases with uncertain cues for classification. Agreement was achieved in 94% of cases by allowing re-review with emphasis on inclusion of an intermediate-grade category. Our study also suggests that pure micropapillary DCIS and apocrine DCIS warrant independent classification as "special type" DCIS. Our small pilot study suggests that, with adherence to specific criteria, most DCIS cases can be easily and consistently classified into the following five categories: (1) high grade, (2) intermediate grade, (3) low grade, (4) pure or predominantly micropapillary, and (5) pure apocrine. Our six observers independently reached a final concordance of 94% despite selection of cases in which consensus in a dichotomous classification was difficult. This was achieved predominantly by accepting an intermediate category of DCIS with intermediate nuclear features and limited necrosis. Confirmation of the applicability of the Modified Lagios Classification awaits completion of a much larger multi-institutional study in which statistical significance and interobserver variation can be better defined.