We studied the prevalence of poor vitamin D status and the association with bone density in men and women born in Norway (quoted as Norwegians, n = 869) and Pakistan (quoted as Pakistanis, n = 177) in the population-based Oslo Health Study, 2000-2001. We measured 25-hydroxyvitamin D, iPTH and ionized calcium in serum and bone mineral density at the forearm site with single energy X-ray absorptiometry. Mean 25-hydroxyvitamin D was 74.8 +/- 23.7 nmol/l in the Norwegians and 25.0 +/- 13.6 nmol/l in the Pakistanis (P = 0.000). The prevalence of secondary hyperparathyroidism (iPTH > or = 8.5 pmol/l, 25-hydroxyvitamin D < 50 nmol/l and Ca2+ < or = 1.35 mmol/l) was four times higher in Pakistani compared to Norwegian women. Also in Pakistani men, serious vitamin D deficiency defined as secondary hyperparathyroidism was prevalent, and five times as frequent as in Norwegian men. However, whereas BMD was significantly lower in Norwegian women with, compared to Norwegian women without, secondary hyperparathyroidism, there was no difference in BMD between Pakistani women with and without secondary hyperparathyroidism. In conclusion, vitamin D deficiency was prevalent among Pakistani immigrants, and in great contrast to the vitamin D replete Norwegians. Serious vitamin D deficiency was interestingly not associated with reduced forearm bone density among Pakistani women.