Prior studies have shown that young patient age at diagnosis is associated with an increased risk of local recurrence among women with ductal carcinoma in situ (DCIS) treated with breast-conserving therapy. Whether this can be explained by differences in clinical or pathologic features of DCIS according to age is an unresolved issue. We compared clinical and pathologic features of DCIS among 657 women in 4 age groups: <45 years (n=111), 45 to 54 years (n=191), 55 to 64 years (n=160), and 65+ years (n=195). DCIS presented as a mammographic abnormality less often in younger than in older women (68%, 82%, 81%, and 86% for women <45, 45 to 54, 55 to 64, and 65+ y, respectively; P=0.003). Among the pathologic features analyzed, DCIS extent as determined by the number of low power fields was greater in younger than in older women (mean number of low power fields were 18.6, 14.2, 10.8, and 11.3 in women <45, 45 to 54, 55 to 64 and 65+ y; P<0.001). In addition, cancerization of lobules was present more often in younger than in older women (77%, 73%, 66%, and 50% for women <45, 45 to 54, 55 to 64 and 65+ y, respectively; P<0.0001). Of note, we found no statistically significant relationship between age and DCIS architectural pattern, nuclear grade, comedo necrosis or expression of estrogen receptor, progesterone receptor or human epidermal growth factor receptor 2. We conclude that DCIS in younger women is more often symptomatic, is more extensive, and more often shows cancerization of lobules than DCIS in older women. Whether these features contribute to the higher local recurrence risk in young women with DCIS treated with the breast-conserving therapy requires further study.