We measured the serum levels of phylloquinone (vitamin K1) and of the menaquinones, MK-7 and MK-8, in a group of 51 women with a mean age of 81 years who were studied within a few hours after a hip fracture. A group of 38 healthy age-matched women randomly chosen from the same population served as controls. Patients with hip fracture had a marked reduction in serum vitamin K1 (336 ± 302 versus 585 ± 490 pg/ml, p < 0.01), MK-7 (120 ± 84 versus 226 ± 178 pg/ml, p < 0.001), and MK-8 (89 ± 113 versus 161 ± 145 pg/ml, p < 0.01), and a large number had undetectable levels, especially of MK-8. Vitamin K levels were not correlated with the time elapsed after fracture or with serum cortisol or other biochemical variables. These data suggest that patients with hip fracture have vitamin K deficiency, an abnormality that could affect bone metabolism through an impairment of the gamma carboxylation of the gla-containing proteins of bone.