Autoimmune endocrinopathies are characterised by an increased number of peripheral blood lymphocytes (PBL) expressing activation/ memory markers on their surface. The aim of this study was to determine whether a similar finding could be detected in a group of 11 paediatric and young adult patients suffering from autoimmune polyglandular syndrome type 1 (APS1), also called autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), as very few data have previously been reported in this field. The control group was made up of 11 sex- and age-matched healthy subjects. Fifteen lymphocyte subsets were compared, in terms of percentage and absolute number, and statistical analysis was performed by the Mann-Whitney test. Measurement of T (CD3+), B (CD19+), natural killer (NK, CD3-CD16/56+), CD4+ and CD8+ T lymphocytes showed that patients with APS1 had a higher percentage and absolute count of T lymphocytes: this was entirely due to the statistically larger CD3+CD4+ fraction. Patients with APS1 also had slightly fewer B and NK lymphocytes, but the difference was negligible. Comparison of CD4+ subpopulations bearing activation and naive/memory antigens (marked by CD69, CD25, anti-HLA-DR, CD45RA and CD45RO) showed that patients with APS1 had generally larger percentages and absolute counts of these subsets: however, only the percentage and absolute size of the CD4+CD25+ subset (p = 0.0354 and p = 0.0151, respectively), and the absolute number of the CD4+ anti-HLA-DR+ and CD4+ CD45RO+ subsets (p = 0.0193 and p = 0.0209, respectively) were significantly higher. Interestingly, patients with APS1 also had significantly fewer CD8+CD11b+ and CD3-CD8+ cells. In conclusion, PBL distribution in APS1 resembles that of other autoimmune diseases. Further studies are needed to confirm and possibly extend these data.