Introduction: Researchers throughout the world are still fascinated by the complex interactions that exist between different physiological parameters and craniofacial shape in the field of orthodontics. One such factor, often overlooked yet significant, is the individual's body weight.

Aim: To assess and compare craniofacial morphology in underweight and normal weight orthodontic patients using cephalometric analysis and BMI.

Materials and Method: 86 patients with the mean age of 15- 25 years were divided into two equal groups of underweight and normal weight groups based on their calculated BMI. Various linear and angular measurements of lateral cephalograms were done using Audaxceph (6.0 version) software.

Results: Mandibular length (Co-Gn) and Corpus length (Go-Pog) were significantly less in underweight individuals than normal weight individuals. No significant difference was found in Midfacial length (Co-A), maxillary length (Co-ANS), (ANS-PNS), cranial base length (S-N) and anterior facial height (N-Me) of both the groups. In vertical dimension anterior facial height (N-Me) and posterior facial height(S-Go) in underweight individuals were somewhat lesser than normal weight patients, but there was no statistically significant difference.