PURPOSE: The purpose of this study is to evaluate the characteristic MR findings of sacrococcygeal pilonidal sinus. MATERIALS AND METHODS: Eight MR images of pathologically proven sacrococcygeal pilonidal sinus were retrospectively reviewed [M: F = 7: 1; age range 9-41 (median, 17) years]. In all cases, a sacrococcygeal mass was present. Five of the eight patients experienced pain, and in three was discharge. MR findings were evaluated with regard to the location and extent of the lesion, and the presence of sinus or cyst, and the results were compared with the pathologic findings. RESULT: According to the clinical manifestations, each case was assigned to one of four groups: the first type (n= 3) showed dermal thickening with subcutaneous fatty infiltration of the ipsilateral natal cleft while pathologically, a follicular cyst with dermal fibrosis and multiple fatty lobules with fibrous septa were found to be present. In the second type (n = 3), fluid was observed in the sinus tract, while the pathologic findings demonstrated the presence of an abscess in this area. In the third type (n = 1), a cystic lesion with airfluid level was present; pathologically, an abscess was revealed. The fourth type (n = 1) showed only a low signal intensity sinus tract on both T1 and T2-weighted images, while the pathologic findings indicated the presence of hairs and follicles within the tract. CONCLUSION: The MR findings of sacrococcygeal pilonidal sinus depend on the clinical manifestation and include subcutaneous fatty infiltration, a sinus tract with or without fluid retention, and a cystic lesion with air fluid level. These findings could be helpful for differentiating between this and other sacrococcygeal lesions.