With the exception of the elderly, there is a dearth of information about the vitamin D status of Irish subjects. Therefore, we assessed the prevalence of suboptimal vitamin D status in a number of age-groups within the Irish population (including females aged, 11-13 years, 23-50 years, 51-69 years, and 70-75 years; and males, aged 20-64 years) during late-winter and late-summer. In females, depending on the age-group studied, between 4 and 19% and between 34 and 85% had an inadequate serum 25 (OH) D level (<50 nmol/l) during late-summer and late-winter, respectively. During late-summer, there was a marked absence of severe and moderate vitamin D deficiency in all subjects, while, 7% of men and, depending on the age-group studied, between 4 and 19% of females had mild vitamin D deficiency. During late-winter, none of the subjects had severe vitamin D deficiency. While none of the men had moderate vitamin D deficiency, 33% of men had mild vitamin D deficiency. In females, depending on the age-group studied, between 32 to 55% of females had mild vitamin D deficiency, and between 2 to 30% of females had moderate vitamin D deficiency, during late-winter. These findings show that inadequate vitamin D status is quite common in healthy Irish subjects, especially and notably so in young girls and more elderly women.