The Morel-Lavallée lesion is an infrequent traumatic lesion that the forensic physician may need to evaluate during examination of a victim. Using a review of the literature and an illustrative case, the objective of this paper is to discuss the medico-legal issues (accountability, functional recovery and healing times, and aftermath) associated with Morel-Lavallée lesions. We describe the case of a 24-year-old motorcycle driver who was hit by a car. Clinically, the right lumbar region had a large 16 × 15 cm ecchymosis with subcutaneous fluid swelling found by palpation. A body scan revealed a Morel-Lavallée lesion among other lesions. On day 7, its thickness was decreased by half. Morel-Lavallée lesions are specifically induced by shearing force with moderate-to-high kinetics in an anatomical area with an underlying fascia. The associated functional disability is globally moderate, but a large lesion or recurrences can extend the time needed to recover. Apart from some exceptions, care without any delay in diagnosis and treatment allows evolution of the lesion without functional consequences, but these lesions are frequently unnoticed in the initial phase.