Rickets in the knee. An 18-month-old boy who was exclusively breastfed lost his appetite after starting nursery school. His mother was aware of the difference of the length of his lower extremities. Posteroanterior radiograph demonstrated indistinct metaphyseal margins in the femur, tibia and fibula (fraying; arrowheads) and the widening of metaphyseal ends in the femur and tibia (splaying; black arrows). Healing stage was suggested due to the provisional zone of calcification although actual onset was unknown. His activated vitamin D level (0.87 pg ml−1) was lower than the paediatric normal range (20–70 pg ml−1).