The term “tarsal coalition” implies a fusion or union of two or more tarsal bones. It is not a rare entity, although a review of the literature might lead one to think this to be the case. The association of this lesion with painful flatfeet and more specifically “rigid flatfoot” makes the roentgenologic diagnosis important. The present paper is devoted to a discussion of coalition involving the calcaneonavicular and the talocalcaneal joints. Review of the Literature Tarsal fusion has long been recognized by anatomists. In 1880, Lagenbech (1) mentioned fusion of the calcaneal and navicular bones. Harris and Beath (2) described a specimen, prepared by John Hunter in 1885, showing bilateral fusion of the talus and calcaneus. Orthopedists have also been aware of tarsal coalition for some time. In 1921, Slomann (3) presented the x-ray findings in several cases of calcaneonavicular fusion. His cases included that of a 13-year-old boy with a six months history of pain in the left foot on walking. Another case was that of a 17-year-old girl with a history of pain in both feet on walking since the age of ten. Both of these patients had fusion of the calcaneus and navicular. In 1948, Harris and Beath (4) reported an incidence of 2 per cent of peroneal spastic flatfoot in the routine physical examination of 3,600 Canadians presenting themselves for army enlistment. This was a third of that for flexible flatfoot. These authors contend that the term “peroneal spastic flatfoot” has become a diagnostic “wastebasket” since painful flatfoot is frequently associated with peroneal pain and muscle spasm. Many orthopedists now agree that peroneal muscle spasm is secondary and not the primary cause of this condition. Badgley (16), Harris and Beath (4), and Coventry (6) believe that “rigid flatfoot” is more frequently due to tarsal anomalies, and they reserve the term tarsal coalition for this entity. It is pointed out that peroneal spasm is associated with inflammatory lesions of the tarsal bones, such as rheumatoid arthritis, with development of a valgus deformity of the feet secondary to peroneal spasm. These authors therefore advocate discarding the term “peroneal spastic flatfoot” for one specifically describing the pathologic changes. Etiology Tarsal coalition is thought to be a congenital anomaly. The term “calcaneonavicular bar,” by usage, includes bony, fibrous, and cartilaginous types of union. These types of union are also implied in the term “talocalcaneal bridge.” Coalition of the calcaneonavicular type may be related to the calcaneus secundarius, a rare sesamoid, occurring between the calcaneus and navicular. This was described by Holl (8) and Pfitzner (9). The latter author points out the relationship of this sesamoid to the os calcis, talus, navicular, and the cuboid. This would imply other possibilities of fusion that we have not encountered. Wagoner (10) reports a case of bilateral fusion of the os calcis and cuboid.