In this study, we evaluated cytomorphologic features of different subgroups of ductal carcinoma in situ (DCIS); we compared seven cytologic features between DCIS and invasive ductal carcinoma (IDC) aspirates to determine whether diagnosis of stromal invasion can be made based on fine-needle aspiration (FNA) findings. There were 142 cases of DCIS and 1,978 cases of IDC enrolled in our study. FNA analysis revealed 80.3% sensitivity for DCIS and 94.7% sensitivity for IDC. High and intermediate grade DCIS exhibited marked nuclear abnormality (92.1% vs. 35.7%, 30.0%; P1 < 0.001, P2 < 0.001) and necrosis (69.7% vs. 0%, 10.0%; P1 < 0.001, P2 = 0.001) in a higher percentage of cases compared to low grade DCIS and intraductal/intracystic papillary carcinoma. The rates of background macrophages (71.3% for DCIS and 21.9% for IDC, P < 0.001) and extensive necrosis (54.0% for DCIS and 16.7% for IDC, P < 0.001) were significantly higher in DCIS compared to IDC. Lymphocytes were observed in conjunction with tumor cells more frequently in IDC (81.3%) compared to DCIS (36.8%, P < 0.001). Stromal fragments associated with tumor cells were only observed in invasive lesions (11.9% micro-invasive DCIS and 52.1% IDC). Tubular structures were found exclusively in IDC (11.5%). Cytologic criteria for diagnosis of high and low grade DCIS are different. The suspicion of DCIS is raised when background macrophages and extensive necrosis are observed. Stromal invasion is suggested by FNA if lymphocytes are entwined around tumor cells or if stromal fragments associated with tumor cells or tubular structures are observed.