Abstract. Serum vitamin K1 concentrations were measured at presentation (just before surgery) and then at weekly intervals for 3 weeks in two groups of elderly patients requiring either hemiarthroplasty for fractured neck of femur (FON, n= 13) or total hip replacement for osteoarthritis of the hip (OA, n= 16). In comparison with healthy elderly volunteers (n= 25), serum vitamin K1 concentrations were significantly lower in both groups at presentation, and fell significantly within 24 h after surgery to concentrations approaching non-detectable, subsequently returning to pre-operative values within 3 weeks. Serum vitamin K1 tended to be lower in the fracture group both before and after operation, although calculation of a vitamin K1–triglyceride ratio reduced the apparent difference as triglyceride concentrations were lower in the fracture group. Osteocalcin concentrations were similar and fell significantly after operation in both groups, returning to pre-operative levels within 7 days. No differences in the two forms of osteocalcin (carboxylated and undercarboxylated) were observed either before or after operation in either group. 25-Hydroxyvitamin D3 concentrations were not significantly different between the two groups at any time. Vitamin K1 status may be lower than desirable in certain groups of the elderly population, and supplementation should be considered as prophylactic therapy.