Abnormalities in the tibial tuberosity were observed in the roentgenograms of thirty-seven male patients on active duty in the military service. These patients were older than those usually described as having the Osgood-Schlatter lesion. Three types of change in the tibial tuberosity could be distinguished in the roentgenograms, and these changes are thought to be definite manifestations of this lesion. The presence of soft-tissue swelling anterior to the tibial tuberosity suggests acute symptoms, whereas a prominent, irregular tuberosity suggests inactive disease. No other correlation between the roentgenographic appearance of the tuberosity and the clinical status of the patient could be made in this age group. Our studies indicate that the etiology of the Osgood-Schlatter lesion in the majority of patients is injury to the lower end of the patellar tendon with resulting new-bone formation.