MRI-guided 'high-intensity focused ultrasound' (MR-HIFU) is a new, image-guided, non-invasive technique which enables treatment of benign and malignant tumours by thermoablation by ultrasound waves. The treatment is completely guided by MRI, which offers advantages for therapy planning, monitoring and visualisation of the treatment result. MR-HIFU has a broad spectrum of applications, including ablation of uterine fibroids, breast cancer, and liver metastases. Most of these applications are still under research. The advantage of the non-invasive character of the treatment is that it can be performed on an outpatient basis and that recovery is fast. The University Medical Center Utrecht, the Netherlands, has a MR-HIFU system that, as well as for pre-clinical experimental applications, is used for clinical treatment of uterine fibroids.