ABSTRACTWe report the case of a 22‐year‐old athlete who sustained a blunt thoracic trauma to the right chest causing a costal cartilage fracture. Plain radiographs revealed no abnormalities while sonographic (US) examination performed a week later because of persistent pain led to the diagnosis of a displaced fracture of the right tenth costal cartilage. A follow‐up US examination confirmed the healing of the fracture and allowed the patient to return to competitive sport activity. We recommend the use of US in patients with persisting pain after thoracic trauma with negative plain radiographs of the ribs to rule out radiographically occult costal cartilage fractures. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:605–607, 2017