OBJECTIVE To study the frequency of ductal carcinoma in situ (DCIS) in a large pathology series. DCIS is a proliferation of non-invasive, malignant epithelial cells within the ductolobular system of the breast. It is a heterogeneous entity with several morphologic variants that differ in gross appearance, growth pattern, cytologic features, mammography, and malignant potential. METHODS The data of The Aga Khan University' Pathology Department, diagnosed on the basis of histopathology, during a 6-year period (1st January 1998 to 31st December 2003) was reviewed, all cases of DCIS studied, and data was analyzed with the help of analytical software SPSS. RESULTS Thirty-eight cases of DCIS were reported to the Aga Khan University Pathology Department, during a 6-year period (1998 to 2003), comprising approximately 1% of all breast cancers reported to the unit in the same period. The mean age of the patients at diagnosis was 48.95 years (CI 95% 44.6; 53.3). Approximately half the cases occurred in the 45-54 year age group (figure 1). Two cases (5.3%) were recurrences with previous lumpectomy scars. Comedo necrosis was observed in five (13.2%) cases, whereas 33 (86.8%) cases were non-comedo type. The clinical presentation was a palpable mass (92.1%), nipple discharge (5.3%) or clinically occult lesions diagnosed on mammography (2.6%). Approximately half the patients presented with a grade 2 disease. Atypical ductal hyperplasia was observed in a third of the cases, predominantly associated with a grade 1 and 2 disease. The estrogen and, progesterone receptor status was studied in 12 (31.6%) cases. Estrogen positivity was observed in 11 (91.7%) cases and progesterone positivity in 7 (58.3%) cases. Microcalcification was observed in four (10.6%) cases. CONCLUSIONS The cases reported in this study are the indolent grade 1 or 2 cases with a non-comedo pattern, and a positive estrogen and progesterone receptor status. If untreated, only 40% of these innocuous forms of DCIS become invasive over a time span of approximately 25-30 years. In Pakistan we are missing the more aggressive forms of DCIS which have a shorter transition to invasive carcinoma.