The objective of this work was to develop an MRI-compatible focused-ultrasound system for preclinical research in small animal models capable of delivering exposures with high spatial precision in a closed-bore clinical imager. A computer-controlled, non-magnetic, 3-axis positioning system was developed using ceramic actuators and linear encoders to position a focused-ultrasound transducer within a clinical MR scanner. Registration between ultrasound and MRI coordinates involves sonicating a tissue-mimicking ultrasound phantom and measuring the centroid of the thermal focal zone with MR thermometry. Linear distances of 5 cm with a positioning resolution of 0.1 mm were achieved for each axis. The system was operated successfully in MR imagers from different vendors at both 1.5 and 3.0 T, and simultaneous motion and imaging was possible without any mutual interference or imaging artifacts. Initial experiments involving opening of the blood-brain barrier at specific targets within the brain suggest a targeting accuracy of 0.4 mm.