We describe two small atypical leiomyomas. The first was a 6-mm de novo lesion in a 53-year-old woman. The second was a 3-mm focus in a 12-mm leiomyoma in a 45-year-old woman. Both lesions showed moderate atypia and a mitotic rate of six per 10 high-power fields. Coagulative necrosis was not seen. Neither patient had received exogenous oestrogen or progestogen. There was no evidence of recurrence or metastasis in either patient after 60 months of follow-up. Our report provides evidence that atypical uterine leiomyomas may arise either de novo or within a leiomyoma.