This prospective Irish observational study examined maternal and infant nutritional supplement use. From an initial sample of 539 mothers recruited from the Coombe Women and Infants University Hospital in Dublin (during 2004-2006), 450 eligible mothers were followed up at 6 weeks and 6 months postpartum. Only 200 women (44.4%) complied with peri-conceptional folic acid at the recommended time with strong social patterning associated with its uptake. Almost 10% of the sample (n = 44) consumed a combined multivitamin and mineral supplement during pregnancy. A vitamin D-containing supplement was provided to only 5 (1.1%) and 15 (3.3%) infants at 6 weeks and 6 months, respectively. A national guideline that advises on adequate and safe use of both vitamin and multivitamin supplements during pregnancy with particular reference to vitamin A and D is warranted. Given the re-emergence of rickets in Ireland, and the reported morbidities associated with vitamin D insufficiency, promoting and monitoring compliance with 200 IU [5 microg] daily vitamin D supplements to all infants particularly those from higher risk groups from birth to 1 year, should be a public health priority.