Collagenous fibroma (desmoplastic fibroblastoma) is a recently described rare benign tumor affecting mainly males in the fifth through seventh decades. This tumor occurs predominantly in the peripheral sites, with predilection for upper and lower extremities. The patients present with a painless mass of involving subcutis, with one quarter of all cases involving skeletal muscle. Both radiographically and histologically these tumors are well-circumscribed small lesions from one to several centimeters in diameter, though lesions as large as 20 cm have been reported. We report a case of collagenous fibroma presenting symptomatically as a 2.4 cm mass within the pedicle and adjacent transverse process of the L5 vertebral segment. Bone erosion by desmoplastic fibroblastoma is very rare event. This tumor should be in the differential diagnosis of the soft tissue lesions presenting with bony erosion.