A professional liability lawsuit of an orthodontic case is presented through its medico-legal assessment. The patient underwent an orthodontic treatment combined with several maxillo-facial surgical interventions. Several temporomandibular joint complications followed, plus he was unhappy with aesthetic results and modifications to his facial features. He wanted to verify from a medico-legal point of view the treatment received as he believed something was not done lege artis. The result of the orthodontic assessment was that there were no indications for such surgical interventions, along with other professional negligence: no psychological support given and no indications as to the aesthetic results postsurgery. It was decided to carry out an orthodontic assessment also on his homozygote twin brother, who was discovered to have the same malocclusion. His medico-legal assessment did not substitute the evidence obtained from the deceased, but gave added weight to the final technical conclusion. Abstract published by arrangement with John Wiley & Sons.