BACKGROUND Studies are conflicting regarding the relationship between ulnar styloid fracture (USF) location and distal radioulnar joint (DRUJ) instability in patients with distal radius fracture (DRF) and concomitant USF. The objective of this study was to determine the association of USF location with TFCC foveal tear and factors associated with DRUJ instability in patients with both DRF and USF. METHODS Fifty-four patients with both DRF and USF who had wrist MRI examination before surgery were analyzed. USF location (tip or base) and TFCC foveal insertion status (intact, partial tear, or complete tear or avulsion with fractured fragment) were evaluated. DRUJ stability was assessed intra-operatively after fixation of the radius. Factors potentially associated with DRUJ instability, such as age, gender, USF location, USF fragment gap, radioulnar distance, radial shortening, and TFCC foveal tear, were analyzed. RESULTS Among 54 patients, 37 (69%) and 17 (31%) had USF at the base and the tip, respectively. In patients with base fractures, TFCC foveal insertion was found to be disrupted in 89% (33/37) patients (complete tear in 11 and partial tear in 22) but intact in 11% (4/37). On the contrary, in patients with tip fractures, the insertion was found to be disrupted in 88% (15/17) patients (complete tear in 2 and partial tear in 13) but intact in 12% (2/17). After fixation of the radius, total 52% (28/54) patients showed DRUJ instability. Especially, DRUJ instability was found in 57% (21/37) of ulna styloid process base fracture patients and 41% (7/17) of ulna styloid process tip fracture patients. In univariate analysis, complete tear of TFCC foveal insertion and wider USF fragment distance were associated with DRUJ instability. CONCLUSIONS Tears of TFCC foveal insertion are common in patients with DRF and concomitant ulnar styloid base fractures. Based on the findings of this study, tear of TFCC foveal insertion seems to be also common in patients with DRF and concomitant ulnar styloid tip fractures. And also, DRUJ instability seems to be associated with a TFCC foveal tear independent of USF location.