PURPOSE OF THE STUDY The study aims to evaluate and compare the results of conservative and operative treatment of individual types of distal ulna fractures associated with distal radius fracture treated by plate osteosynthesis and to verify the conclusions of the other authors regarding the recommended therapeutic procedures in these fractures. MATERIAL AND METHODS In the period from 08/2013 to 09/2015, a total of 81 patients participated in the prospective randomised study, with the mean follow-up period of 24 months (6-36). All the fractures of distal two thirds of ulnar styloid process were treated conservatively. The patients with the other types of ulnar fractures (fractures of the proximal third of ulnar styloid process, ulnar head fractures, subcapital fractures) were systematically divided into two cohorts, based on which the subsequent (conservative vs. operative) treatment of distal ulna fractures was indicated. The operative treatment of all the types of distal ulna fractures was performed by plate osteosynthesis using LCP Distal Ulna Plate implant so that a uniform method is applied. RESULTS In the post-operative follow-up not a single patient with tip fracture of ulnar styloid process in the cohort showed a posttraumatic instability or disorder of distal radioulnar joint (DRUJ) biomechanics (ROM 96.6% (91-100), MWS 61.3 points (75-100), QDASH 2.9 points (0-6.8)). The patients with a fracture of the proximal third of ulnar styloid process, a fracture of ulnar head and a subcapital fracture, treated operatively, achieved better early radiographic and functional outcome (ROM 95.7% (60-100), MWS 91.2 points (75-100), QDASH 3.5 points (0-11.4)) than patients treated conservatively (ROM 89.6% (64-100), MWS 70.4 points (35-85), QDASH 18.4 points (0-52.3)). DISCUSSION The study confirms the conclusions drawn by the other authors that tip fractures of ulna do not cause posttraumatic DRUJ instability and do not require operative treatment. Conservative treatment of ulnar base fractures led to non-union in 60% of cases and to malunion in 25% of cases, altogether in 15 patients (75%) the clinical examination revealed a conclusive posttraumatic DRUJ instability of various severity and these patients showed healing in malunion ad latus greater than 2 mm and non-union of the fracture. By performing anatomical reduction and osteosynthesis of ulnar "base fractures", the stability and DRUJ function were restored in all the patients, thus also a better functional outcome was attained. Conservative treatment of ulnar head fractures brought worse outcomes due to malunion of fractures resulting in a noncongruent articular surface of DRUJ or a change in axial position of the distal end of the bone. The change in DRUJ biomechanics resulted in a limited rotation of radius and a limited range of forearm mobility. The operative treatment of subcapital ulna fracture had a very good early outcome as compared to conservative treatment of the fracture which healed in malunion, the change of axial position of the distal end of the bone resulted in a limited range of forearm mobility. CONCLUSIONS Based on the early functional and radiographic outcomes of RCT study it can be stated, in agreement with the other authors, that the operative treatment of distal ulna fractures associated with the distal radius fracture treated by ORIF should be indicated for base fractures of ulnar styloid process associated with DRUJ instability following the osteosynthesis of distal radius fracture and peripheral fragment dislocation ad axim or ad latus in radial direction by 2 mm and more, and also in case of displaced ulnar head fractures and instable and displaced subcapital fractures of the ulna. Key words: distal ulna fracture, plate osteosynthesis, LCP distal ulna plate.