Introduction: Vitamin D is essential for bone health. We aimed to assess the vitamin D levels of patients undergoing total knee arthroplasty TKA). Methods: All TKA patients during a calendar year had their 25-hydroxyvitamin-D3 (25-OH-D3) assay levels assessed pre and post operatively. A control group comprising of patients admitted for 1-day general medical assessment was recruited. Usage of supplements containing Vitamin D was recorded for both groups. Results: There was no evidence of a difference in Vitamin D levels between the TKA group and the control group (p=0.19). Just over 40% of patients had insufficient levels of vitamin D in the TKA group (50 nmol/L cut off). There was a statistically significant drop in vitamin D levels post operatively (p=0.0001). Supplements were protective against insufficiency post operatively (p=0.0005, OR 6.0985). Discussion: This study documents a high prevalence of vitamin D insufficiency in patients undergoing TKA surgery. Our results suggest a consumption of 25-OH-D3 as part of the surgical insult.