BACKGROUND Some basal ulnar styloid fractures (USFs) achieve union without surgical fixation when accompanying distal radius fractures (DRFs) are treated via placement of volar locking plates (VLPs). The purpose of this study was to seek factors predictive of such healing through the retrospective case-control study. METHODS We evaluated 203 patients who received VLPs to treat DRFs in our institute from March 2010 to February 2018; Group 1 contained "union" patients and Group 2 contained "nonunion" patients. Basic demographic, radiological, and operative variables were compared. At the final follow-up (at least 2 years postoperatively), pain was scored using a visual analog scale (VAS). Scores on the Disabilities of the Arm, Shoulder, and Hand (DASH) instrument; grip strengths; and demerit points of the Gartland and Werley system were compared between groups. RESULTS Group 1 consisted of 58 patients and Group 2 consisted of 147 patients. Univariate analysis showed that age, bone mineral density (BMD), and Gaulke USF classification significantly differed between groups (all p < 0.05). Multivariate analysis showed that BMD (p < 0.001, odds ratio [OR] = 0.214, 95% confidence interval [95% CI] = 0.126-0.363) and Gaulke classification (p < .001, OR = 0.092, 95% CI = 0.034-0.250) were significantly associated with USF union, which was significantly higher in patients with mean BMD ≥ -0.12 (the cutoff value) and type IIC USFs. However, postoperative clinical outcomes at the final follow-up did not differ significantly between groups (all p > 0.05). CONCLUSIONS Approximately 30% (58/205) of basal USFs associated with DRFs united after VLPs alone were placed to treat the DRFs. BMD ≥ -0.12 independently predicted union. Type IIC USFs exhibited more union than other fracture types. Additional surgical fixation of a basal USF accompanied by a DRF treated via VLP placement may be unnecessary, especially if BMD is good and fracture type is IIC. METHODS Level III, Case-control study.