Maternal vitamin D insufficiency is associated with childhood rickets and longer-term problems including schizophrenia and type I diabetes. Whilst maternal vitamin D insufficiency is common in mothers with highly pigmented skin, little is known about vitamin D status of Caucasian pregnant women. The aim was to investigate vitamin D status in healthy Caucasian pregnant women and a group of age-matched non-pregnant controls living at 54-55 degrees N. In a longitudinal study, plasma 25-hydroxyvitamin D (25(OH)D) was assessed in ninety-nine pregnant women at 12, 20 and 35 weeks of gestation, and in thirty-eight non-pregnant women sampled concurrently. Plasma 25(OH)D concentrations were lower in pregnant women compared to non-pregnant women (P<0.0001). Of the pregnant women, 35, 44 and 16% were classified as vitamin D deficient (25(OH)D < 25 nmol/l), and 96, 96 and 75% were classified as vitamin D insufficient (25(OH)D < 50 nmol/l) at 12, 20 and 35 weeks gestation, respectively. Vitamin D status was higher in pregnant women who reported taking multivitamin supplements at 12 (P<0.0001), 20 (P=0.001) and 35 (P=0.001) weeks gestation than in non-supplement users. Vitamin D insufficiency is evident in pregnant women living at 54-55 degrees N. Women reporting use of vitamin D-containing supplements had higher vitamin D status, however, vitamin D insufficiency was still evident even in the face of supplement use. Given the potential consequences of hypovitaminosis D on health outcomes, vitamin D supplementation, perhaps at higher doses than currently available, is needed to improve maternal vitamin D nutriture.