OBJECTIVE: The objective was to look for the incidence and clinicopathologic findings of women in whom the diagnosis of endometrial stromal sarcoma was initially missed. METHODS: We carried out a retrospective analysis of cases treated at our institution from 1990 to 2002. RESULTS: In 6/15 (40%) women suffering from endometrial stromal sarcoma, the diagnosis initially was missed. The first diagnosis was uterine leiomyoma (n = 2), myxoid leiomyoma (n = 2), cellular leiomyoma (n = 1), or lymphatic disorder (n = 1). The final diagnosis was only made after consultation of a pathologist with a special interest in gynecological oncology. The mean age of this group was only 34 years (range, 18-53). A mean delay in diagnosis of 143 months (range, 24-408) resulted in stage 4 disease in 5/6 women. After a mean follow-up of 16 years (range, 5-43), 4/6 are without macroscopic evidence of disease, 1/6 with evidence of disease, and 1/6 died of disease. CONCLUSION: Especially in younger women, the diagnosis of endometrial stromal sarcoma can be problematic.