Health policy in North America advocates that all breastfed infants receive a vitamin D supplement of 400 IU per day for the primary prevention of rickets. Despite this recommendation, rickets still occurs in Canada. It is not known whether vitamin D deficiency in the Canadian population is solely attributable to inadequacies in vitamin supplementation. Thus, the evaluation of current practices, including awareness and compliance with recommendations, is clearly needed. The objective of this study was to describe the vitamin D supplementation practices of mothers of newborns living in the Montreal area. This was a cross-sectional telephone survey of 343 mothers delivering a healthy term infant from December 2007 to May 2008 at the Royal Victoria Hospital (Montreal, Que.). Ninety percent of all mothers breastfed their infants during the first 6 months; 53% did so exclusively. Of mothers exclusively breastfeeding, 74% reported meeting the Health Canada recommendation. The main reason for not adhering to the recommendation was the assumption by mothers who began to feed fortified formula (400 IU.L-1) that supplementation was no longer necessary. Fifty percent of infants receiving mixed feedings without supplementation prior to 6 months did not achieve the recommended intake. Receiving advice about supplementation and the higher education of mothers were significant positive determinants of supplementation practices. This work identified infants consuming mixed feedings and those consuming only formula in the first 6 months as groups at high risk for not meeting the recommended 400 IU.day-1 of vitamin D. Therefore there may still be gaps in knowledge regarding vitamin D supplementation.