BACKGROUND The purpose of this study was to evaluate a new stereotactic method for preoperative coil-marking of musculoskeletal tumors with use of interventional magnetic resonance imaging. METHODS Nine patients with a soft-tissue or bone-marrow tumor were referred to our department for preoperative marking of the extent of the lesion. In one patient, two lesions were marked. Guidance for the punctures and the delivery of the coils was provided by an open low-field magnetic resonance imaging system with horizontal access. After imaging of the extent of the lesion, magnetic resonance imaging-compatible titanium coils were placed with use of nearly real-time or step-by-step magnetic resonance imaging control. The coils were placed up to seventy-two hours before the surgery. The inclusion of the tumor borders within the area of the excision was examined with cross-sectional histological analysis of surgical specimens. RESULTS The tumor-marking intervention was successfully performed with the guidance of magnetic resonance imaging only in all patients. Preoperatively, nineteen coils were used to mark the ten lesions in the nine patients. All of the coils were easily located with intraoperative fluoroscopy. No coil migrated between the time of the percutaneous marking and the surgery. Histological examination of the resection borders revealed no residual tumor cells. No complications were observed, and, after a mean of twenty-three months of follow-up, no tumor had recurred. CONCLUSIONS Preoperative coil-marking guided by magnetic resonance imaging for exact delineation of a musculoskeletal tumor is technically feasible and can readily demonstrate the full extent of the tumor. Use of magnetic resonance fluoroscopy reduces the time needed for the intervention. We recommend the coil-marking technique.