Certain subtypes of in-situ carcinoma can be more difficult to recognize than others. Solid papillary carcinoma in-situ can show cytological and architectural features that overlap with those of usual ductal hyperplasia, and apocrine proliferations are often challenging due to less familiarity with the criteria for apocrine atypia. Non-classical examples of lobular carcinoma in-situ, such as florid or pleomorphic, may be difficult to distinguish from ductal carcinoma in-situ. The unique histologic features, diagnostic criteria, ancillary immunohistochemical findings, and clinical management of these challenging subtypes of in-situ carcinoma will be reviewed.