We report the case of a 34-year-old man who presented with a 4-year history of a soft tissue on the palmar aspect of the thumb. Magnetic resonance imaging demonstrated the presence of a mass with heterogeneous high intensities on T1-weighted images and high intensities on T2-weighted images. We performed excisional biopsy. Histologically, the tumor was composed of mature adipocytes and spindle cells in a collagen background. Immunohistochemically, the tumor cells showed strong expression of CD34. Therefore, we diagnosed it as spindle cell lipoma. To the best of our knowledge, only 2 cases of spindle cell lipoma of the thumb have previously been reported.