Microwave endometrial ablation (MEA) is an effective treatment for menorrhagia and several reports have established its efficacy in treating menorrhagia. However, according to recent reports, relapse of menorrhagia can be one of the long-term clinical outcomes following MEA and often necessitates re-surgery. The authors present the case of a patient with severe abdominal pain for over a month due to a sudden enlarging myoma. Two and a half years prior, she had undergone MEA. Therefore, the patient needed an emergency hysterectomy. This is the first reported case of a rapidly enlarging myoma following MEA. Therefore, a patient who has undergone MEA must be followed up closely for at least three years.