Objective: To test the null hypotheses that children with unilateral agenesis of the mandibular second premolar (MnP2) do not show (1) greater distal angulation of the unerupted antimere and (2) delayed tooth formation compared with children without agenesis. Materials and Methods: Panoramic radiographs of 38 patients with unilateral aplasia of MnP2 were retrospectively examined and compared to a non-agenesic control group of 82 patients. Ages ranged from 8 to 15 years. Contralateral mandibular deciduous second molars were present for all participants. Each unerupted MnP2 was traced, and its developmental stage and angulation were recorded (measured with the distal angle and the premolar-molar angle). Dental age was evaluated using the Haavikko method. Student's t-test was performed to identify significant differences between the compared groups. The significance level for statistical testing was set at P , .05. Results: The results indicated a 9.5u decrease in the distal angle and a 13.2u increase in the premolar-molar angle for the unerupted MnP2 in the agenesis sample. This was a highly statistically significant difference (P , .001 and P , .0001, respectively) compared with the MnP2