In fifteen patients, a subtle injury of the Lisfranc joint (tarsometatarsal articulation) was found. The lesion was defined as a diastasis of two to five millimeters between the bases of the first and second metatarsals, as seen on anteroposterior radiographs. There often was a long delay between injury and diagnosis. Eight patients were treated with a below-the-knee cast only, three had treatment with a cast and then tarsometatarsal arthrodesis, two had no initial treatment but later had arthrodesis, and two had open reduction and internal fixation. The duration of follow-up ranged from two to thirteen years after the diagnosis. There was no correlation between the severity of the diastasis and the patient's functional result. Marked disability and pain persisted in seven patients, and six of them had flattening of the longitudinal arch. Maintenance of the longitudinal arch usually was associated with a better functional outcome. When a patient has a subtle injury of the Lisfranc joint, weight-bearing lateral radiographs of both feet are needed to identify flattening of the longitudinal arch. Such radiographs should be made routinely in the evaluation of all injuries of the foot that may involve the Lisfranc joint.