Objectives: The objectives of this study were to examine variations in the cross-sectional morphology of the mandible at the premolar region. Materials and Methods: Two hundred and forty-three cone-beam computed tomography datasets, providing 486 sites, were reviewed to examine the cross-sectional morphology of the mandible in the premolar region. Results: A lingual concavity was detected in 14% of the sites examined. A buccal cavity was present in 17.9% of sites. In the presence of a buccal concavity, there was a statistically significant association between increased mandibular height (P = 0.002) and increased crest to neurovascular bundle distance (P < 0.001). There was no statistically significant difference in the mandibular height or ridge crest to the neurovascular canal distance, where there was a lingual concavity. The most common cross-sectional shapes observed in the premolar region of the mandible were straight-convex (26.3%), convex-convex (24.1%), and straight-straight (21.6%). The least common shapes were convex-concave (10.1%) and concave-concave (3.9%). Conclusions: In this study, 28% of mandibular premolar sites had a concavity in the buccal and/or lingual cortical plate. It is clear that the lower premolar regions require considerable three-dimensional pre-implant planning not only due to the complex neurovascular elements but also due to the frequent presence of concavities in the buccal and/or lingual plates.