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Collagenous fibroma is an uncommon benign soft tissue lesion that has a wide anatomic distribution. We describe a case of a collagenous fibroma that appeared in the left soft and hard palate of a 37-year-old woman as a 5.0-cm solitary, firm nodule. Microscopically, it was composed of stellate or spindle-shaped cells embedded in hypovascular fibrous stroma. Entrapment of fat was focally identified at the edges. Mitotic figures and tumor necrosis were absent. Tumor cells were immunopositive for vimentin, and a few cells were positive for α-smooth muscle actin. Tumor extracellular matrix was immunopositive for type I and type III collagen, as well as for fibronectin. These findings satisfied the diagnostic criteria for collagenous fibroma (desmoplastic fibroblastoma). This case, to our knowledge, represents the first report of this tumor in the mouth. The differential diagnosis of fibrous lesions of the mouth is discussed.