Objective: The objective of this study is to determine the mid-term effect of MRgFUS (Magnetic Resonance-guided Focused Ultrasound Surgery) focusing on the volume reduction ratio and the perfused volume of uterine fibroid. Material and Methods: Forty-three fibroids on 30 patients were examined, excluding the case treated with GnRHa (gonadotropin releasing hormone analogue) just before MRgFUS. The fibroid’s volume and the perfused volume were measured by MR images on the treatment day and then again 6 months later. The fibroids were classified into 3 types according to the signal intensity on T2-weighted MR images; Type 1, low intensity as skeletal muscle; Type 2, intermediate intensity that is lower than myometrium but higher than skeletal muscle; Type 3, high intensity that is the same as or higher than myometrium. Result: The non-perfused ratio immediately after MRgFUS was significantly lower in Type 3 fibroid as we had previously reported. The non-perfused volume of Type 3 fibroid showed a tendency to shrink more at 6 months after MRgFUS, than the other two types, however the volume reduction ratio was smallest in Type 3 fibroid (p<0.01). At the same time, some fibroids showed smaller perfused volume 6 months later than on the treatment day; those generally belonged to Type 1 and Type 2. Conclusion: The volume reduction ratio indicates the Type 3 fibroids respond less well to MRgFUS. This ratio could be affected by the reduction of the non-perfused volume, but also reduction or increase of the perfused volume. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]