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Pregnancy and post-partum represent a period of susceptibility for vitamin D insufficiency. This study investigated S-25 [OH] D levels in women in northern Sweden 4 weeks post-partum and its association with selected background factors. Blood from 100 healthy women were analyzed for iron status and serum levels of S-25[OH] D using ionization-mass spectrometry (HPLC-APCI-MS). <50 nmol/L was categorized as insufficiency and <25 nmol/L as deficiency. Maternal BMI, dietary habits, fungal infections during pregnancy, and infant birth characteristics were collected using questionnaires and medical charts. 58% were vitamin D insufficient whereas 10% had deficiency. Insufficiency was most common during winter (OR = 2.77; 95% CI = 1.1-6.96) and women with deficiency reported lower milk consumption; 11.3 ± 22.8 intakes per months vs. 34.0 ± 28.9 for those above 25 nmol/L (p < 0.05). Vitamin D-insufficient women had lower serum ferritin levels (p < 0.01) and higher serum transferrin levels (p < 0.05). A history of vaginal fungal infection during pregnancy was associated with insufficiency (OR = 5.10; 95% CI = 1.01-25.73), however, the confidence interval of the estimate was wide, resulting in uncertainty. It is concluded that vitamin D insufficiency 4 weeks post-partum was common in women living at 63°49'N. The odds of being insufficient were increased during winter whereas milk consumption was negatively associated with deficiency. The low vitamin D-levels particularly during winter is a public health concern. From a public health perspective it has to be considered whether dietary advices alone should be modified or if supplementation with vitamin D during pregnancy and the post-partum period also is needed.