To detect precise anatomical configuration of the first ray in feet with hallux valgus, a two-dimensional coordinate system was devised for evaluation of a weight-bearing dorsoplantar radiograph. The radiographs, taken from 229 feet of 114 patients with symptomatic hallux valgus and 94 normal feet, were investigated. A comparative study showed the first metatarsal head of a foot with hallux valgus was located on the medial side of that of the normal foot and the base of the proximal phalanx of the hallux valgus foot was located on the same point of that of the normal foot. Lateral translation of the base of the proximal phalanx occurred only in cases with overlap toes. Our study shows that subluxation of the metatarsophalangeal joint in hallux valgus is primarily caused by metatarsus primus varus. This study indicated that first metatarsal osteotomies should be given the first priority in consideration for bunion surgery, because these procedures could move the first metatarsal heads laterally in a more normal position.