PURPOSE: To evaluate the usefulness of diffusion-weighted imaging after intracranial surgery in patients with intracranial tumors. MATERIALS AND METHODS: Within ten days of intracranial surgery, diffusion-weighted MR images were obtained in 68 patients with intracranial tumors which included meningioma (n=31), glioma (n=21), neurogenic tumor(n=4), hemangiopericytoma (n=3), and in three cases involved metastasis. The signal intensity of the resected margin and adjacent parenchyma was visually assessed on diffusion-weighted images, and the signal intensities on seen T1-and T2-weighted images were also analyzed. In patients with newly developed hyperintense lesions in parenchyma adjacent to the resection sites seen on postoperative T2-weighted images, apparent diffusion coefficients (ADC) were calculated and analyzed on follow-up MR images. RESULTS: Immediate postoperative diffusion-weighted images showed various signal intensities at the resected margins visible on conventional and diffusion-weighted MR images. In 15 patients, newly developed hyperintense lesions adjacent to resected sites were seen on postoperative T2-weighted images. On diffusion-weighted images, nine of these lesions were hyperinteuse and and were shown by follow-up MR imaging to be subject to focal tissue loss and atrophy, and six were isointense but with no sign of tissue loss or atrophy. Among the 15 patients with postoperative lesions near the site of tumorectomy, diffusion-weighted imaging showed that the ADC values of hyperintense lesions were significantly lower than those of isointense lesions (independent sample t-test: p<0.05). CONCLUSION: In patients with intracranial tumors, immediate postoperative diffusion-weighted imaging is useful for differentiating between ischemic tissue damage and vasogenic edema.