Hypermobility of the first ray, which is caused by an instability of the first metatarsocuneiform joint, is one of the factors that induces hallux valgus and can be caused by technical mistakes in ballet practice. Correlation between ballet practice and hypermobility of the first ray. Using a modified Klaue device, mobility of the first metatarsocuneiform joint was measured (hypermobility ≥ 10mm) in both dorsal and dorso-medial directions in 264 feet in 2 groups of people: ballet dancers (non professional) and a control group of non-dancers. 45° mobility is statistically higher than dorsal mobility, and mobility in the ballet dancer group is higher than in the control group, but there is no correlation between hours of ballet and en-pointe shoe practice, and hypermobility of the first ray. First ray hypermobility, and even hallux valgus, in ballet practice is related to anatomical-hereditary factors and to incorrect technical execution.