This study was conducted to evaluate the vitamin D status of healthy breastfed Pakistani infants and their nursing mothers. Sixty-two breastfed healthy infants and their nursing mothers belonging to the upper and lower socioeconomic classes were examined. Serum 25-hydroxy vitamin D [25(OH)D], serum calcium, phosphorus and alkaline phosphatase were measured. The mean serum 25(OH)D in infants was 34.59 +/- 26.56 nmol/l. Fifty-five percent of infants and 45% of mothers had very low serum 25(OH)D levels (<25 nmol/l). Significantly higher levels were found in infants of lower socioeconomic class (p < 0.001) and in those living in mud houses (p = 0.002) and infants >6 months (p < 0.001). A high prevalence of vitamin D deficiency was found in breastfed infants and nursing mothers, predominantly among those belonging to the upper socioeconomic class. Infants of the lower socioeconomic class had comparatively higher serum 25(OH)D levels, but even these levels were below the normal range for infants (90 +/- 27.5 nmol/l).