Objective To investigate the impact on distal radioulnar joint(DRUJ) stability by various types of ulnar styloid fractures surgically and non-surgically treated.Methods A total of 150 cases of ulnar styloid fractures treated between August 2001 and May 2010 were involved in this study.There were 68 cases of type Ⅰ fractures and 82 cases of type Ⅱ fractures.Preoperative radiographic measurements,postoperative evaluation of DRUJ stability and wrist function were carried out.Results Preoperatively spacing of the DRUJ was measured on standard lateral wrist Ⅹ-Rays when the distance from the pisiform to the scaphoid was less than 3 mm.The spacing was less than 5 mm in type Ⅰ fractures and more than 5 mm in type Ⅱ fractures.All the patients were follow-up for 26 to 102 months,with an average of 70 months.There was no relaxation of the DRUJ among 68 type Ⅰ cases,whereas DRUJ relaxation occurred in 11 of the 82 type Ⅱ cases.Evaluation of wrist function using Green-O'Brien evaluation criteria revealed excellent results in 12 and good results in 11 of the 28 type Ⅰ ulnar styloid fracture cases treated surgically.The overall satisfactory rate of this cohort was 82.1%.Of the 40 non-surgically treated type Ⅰ cases,results were rated as excellent in 10 cases and good in 19 cases,with an overall satisfactory rate of 72.5 %.72 of type Ⅱ ulnar styloid fractures were surgically treated leading to excellent results in 62 cases and good results in 6 cases,with a 94.4% satisfactory rate.Non-surgical treatment of the other 10 type Ⅱ cases led to excellent results in 1 case and good results in 2 cases,achieving a 30.0% satisfactory rate.Conclusion Type Ⅰ ulnar styloid fractures have less impact on DRUJ stability than type Ⅱ fractures.Type Ⅱ ulnar styloid fractures therefore should be surgically treated to achieve anatomical reduction and preserve DRUJ stability. Key words: Fracture,bone; Wrist joint; Treatment outcome; Ulnar styloid