An 8-year-old intact male Briard was presented with a non-painful bilateral diffuse swelling of mandibleand maxilla. The teeth were mobile. The jaws felt like rubber. Radiographic examination revealed generalizedosteopenia. Ultrasound showed prominent parathyroid glands. The plasma parathyroid hormone concentrationwas extremely high, the serum 25-hydroxy-vitamin D (25-OH Vit D) was low, and the serum ionized calciumremained within the reference range. As the dog had been fed an unbalanced homemade diet for manyyears, rubber jaw, osteomalacia and secondary hyperparathyroidism due to dietary calcium and vitamin Ddeficiency were diagnosed. Dietary correction resulted in clinical improvement and normalization of the plasmaparathyroid hormone concentration within 4 months. However, although the 25-OH Vit D was clearly raised,it still did not reach reference values, which was due to lack of owner compliance, as the owner had changedthe patient’s diet over time.