Pilomatricoma is an uncommon benign skin neoplasm arising from the hair matrix. The radiologic features of this uncommon tumor have occasionally been described in the literature however, to the best of our knowledge, there have been no reports in Korea on the sonographic and MR imaging findings of pilomatricoma involving the upper arm. In this article, we describe the imaging findings of a case of pilomatricoma involving the upper arm, with the emphasis being placed on the sonographic and MR imaging findings and a review of the literature.