Objectives. The aims of this study were to determine the incidence of malignant polyps in stage 1A endometrial cancer, to define the pathological features of such cancers, and to assess whether clinical outcome differs from similar cancers without a malignant polyp. Methods. We performed a retrospective pathological review of 107 cases of stage 1A endometrial cancer treated at two centers in New South Wales between January 1988 and July 2003. The presence of a malignant polyp was determined and a pathological description made of the tumor. Clinical data were collected, including prior tamoxifen usage, tumor recurrence and survival. The outcome of the malignant polyp group was compared to the same histological subtype not involving a malignant polyp. Results. The incidence of malignant polyps in our series was 32% . Malignant polyps occurred in all 8 cases involving a serous subtype. Precursor lesions of endometrial cancer were identified within malignant polyps. Three out of the four recurrences occurred in high-grade tumor subtypes and all four had a large primary tumor (size ≥ 4 cm). When comparing the same subtype of tumor with and without a malignant polyp, there was no significant difference in clinical outcome. Conclusions. Approximately one-third of stage 1A endometrial cancers are associated with a malignant polyp. Serous carcinoma commonly arises within an otherwise benign endometrial polyp. Malignant polyps offer an opportunity to identify precursors of endometrial carcinoma. Clinical outcome of stage 1A endometrial carcinoma was related to the histological subtype and the size of the tumor rather than the presence of a malignant polyp. Objectives. The aims of this study were to determine the incidence of malignant polyps in stage 1A endometrial cancer, to define the pathological features of such cancers, and to assess like clinical probabilities different from similar cancers without a malignant polyp. Methods. We performed a retrospective pathological review of 107 cases of stage 1A endometrial cancer treated at two centers in New South Wales between January 1988 and July 2003. The presence of a malignant polyp was determined and a pathological description made of the tumor. Clinical data were collected, including prior The outcome of the malignant polyp group was compared to the same histological subtype not involving a malignant polyp. Results. The incidence of malignant polyps in our series was 32%. Malignant polyps occurred in all 8 cases involving a serous subtype. Precursor lesions of endometrial cancer were identified within malignant polyps. Three out of the four r When comparing the same subtype of tumor with and without a malignant polyp, there was no significant difference in clinical outcome. Conclusions. Approximately one -third of stage 1A endometrial cancers are associated with a malignant polyp. Serous carcinoma usually arises within an otherwise benign endometrial polyp. Malignant polyps offer an opportunity to identify precursors of endometrial carcinoma. Clinical outcome of stage 1A endometrial carcinoma was related to the histological subtype and the size of the tumor rather than the presence of a malignant polyp.