Introduction: Impairment of mandible mobility model is one of the criteria for clinical diagnosis of temporomandibular joint (TMJ) disc displacement. Objectives: Analysis of the range and pattern of the mandibular opening in patients with anterior disc displacement without reduction. Material and methods: According to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) the range and pattern of mandibular opening were analyzed in 49 patients (45 women and 4 men) with uni- and bilateral anterior disc displacement without reduction on MR imagines. Results: The average range of opening in patients with unilateral lack of disc reduction was 33.74 mm, and 28.93 mm in patients with bilateral lack of reduction. The difference between the average range of opening in both groups was statistically significant (p<0.05). Uncorrected mandibular deviation was the most frequent opening pattern in patients with unilateral lack of reduction (19 out of 35 cases). In 11 out of 14 cases with bilateral lack of reduction the straight opening pattern was found. Conclusions: TMJ disc displacement with bilateral lack of reduction during opening can cause greater opening limitation than unilateral lack of reduction. Anterior disc displacement without reduction in the MR images can clinically present with limitation of mandibular opening as well as correct range of this movement, which can cause difficulties in the clinical diagnosis of these problems.