Assessment and treatment of osteoporosis are recommended following hip fracture. Osteoporosis treatment assumes an adequate calcium intake and a normal vitamin D plasma level. The authors conducted a study in three phases. Phase I: circulating 25-hydroxyvitamin D levels were retrospectively recorded from in the case records of 381 consecutive patients with 387 hip fractures, between March 2010 and September 2011. Only 27 patients had sufficient (> 75 nmol/L) circulating vitamin D, and of these 22 were taking vitamin D supplements. The remainder, 354 patients, had abnormally low vitamin D levels, with a mean value of 26.4 nmol/L. These findings confirmed literature data, and gave rise to the prospective Phase II (October 2011): 14 consecutive patients with a hip fracture received rapid substitution therapy with 50,000 IU cholecalciferol (vitamin D3) daily for 3 days. Patients with corrected calcium level (calcium level based on the serum albumin level) > 2.60 mmol/L were excluded from phase II (and phase III), in order to avoid hypercalcemia. Substitution resulted in an increase in vitamin D plasma levels from +/- 29.6 nmol/L to +/- 81.4 nmol/L (p < 0.0001), after +/- 14 days. However, vitamin D level remained below the desired threshold of 75 nmol/L in 29%. Therefore it was decided to increase the treatment period from 3 days to 7 days in the next 54 patients with a hip fracture in a prospective phase III (October 2011-January 2012). This time rapid substitution resulted in an increase from +/-31.4 nmol/L to +/-131.1 nmol/L (p < 0.0001), after +/- 16 days, and 100% of treated patients achieved plasma levels above the desired threshold of 75 nmol/L. virtually all patients with a hip fracture have low vitamin D plasma levels; substitution with 50,000 IU oral cholecalciferol daily for 7 days increases vitamin D plasma levels rapidly, safely and consistently.