BACKGROUND : Breast cystosarcoma phyllodes tumors are rare and can be benign or malignant. All sub-divisions of phyllodes tumor-benign, borderline and malignant, can harbor carcinomas, although the incidence is extremely rare. METHODS : We present two nonconsecutive cases of coexisting ductal carcinoma in situ (DCIS) and phyllodes breast tumors in young patients. UNASSIGNED : Retrospective review of two patient's medical record was performed. CASE 1: 30-year-old female underwent excisional biopsy for 3.48 cm mass found on ultrasound. Pathology revealed malignant phyllodes tumor with positive margin. On re-excision, patient was found to have 1.5 cm area of ductal carcinoma in situ (DCIS) with positive margin. Patient then underwent re-reexicision of DCIS with negative margin. Patient underwent chemotherapy and tamoxifen for three years without evidence of disease. CASE 2: 30-year-old female presented with 1.3 cm lesion found on ultrasound which core needle biopsy revealed a fibroepithelial tumor. Patient subsequently underwent excision biopsy which found 1.5 cm benign phyllodes tumor and 3.5 mm DCIS within the phyllodes tumor with negative margins. Patient declined additional chemotherapy or hormonal therapy and is currently considering mastectomy. CONCLUSIONS : Phyllodes tumors are rare and ones with a coexisting carcinoma are even less frequently encountered. The treatment plan can change upon diagnosis of the carcinoma via the pathology. Treatment should be guided by the type and stage of carcinoma detected which may include additional surgical resection and lymph node sampling.