A study examined the relationship between preoperative vitamin D deficiency and delayed neurocognitive recovery in older women (65 years and older) undergoing major gynecologic surgery. A prospective cohort study included 156 patients with a mean vitamin D level of 37.6 ± 18.7 nmol/l, and 73.7% of them had vitamin D deficiency (level below 50 nmol/l). Vitamin D-deficient patients had a higher incidence of delayed neurocognitive recovery on the fifth postoperative day compared to non-deficient patients (22.6% vs. 7.3%). The analysis showed that vitamin D deficiency increases the risk of delayed recovery approximately fivefold and that acute systemic inflammation plays a partial role in this relationship. Acute systemic inflammation accounted for 15.2% of the total effect of vitamin D deficiency on delayed neurocognitive recovery. The results suggest that preoperative vitamin D deficiency is associated with an increased risk of neurocognitive complications after surgery in older women.