IntroductionA hydatid cyst of the breast is rare and often goes unnoticed by mammography and ultrasound. Preoperative diagnosis may be performed using fine-needle aspiration cytology, which also minimizes the risk of intraoperative rupture.Case presentationWe report the case of a 70-year-old Spanish woman who was diagnosed with a hydatid cyst using fine-needle aspiration cytology before surgery.ConclusionFine-needle aspiration cytology is an accurate and safe technique that can allow surgery to be avoided, especially in older patients or patients with high surgical risk.