Dexamethasone is frequently administered to surgical patients for anti-emetic prophylaxis. We have examined the immunomodulatory effects of a single bolus of dexamethasone on circulating peripheral blood mononuclear cells (PBMCs) in the same 10 healthy male volunteers, previously used in our investigation on early effects of a single anti-emetic dose of dexamethasone on innate immune cell gene expression and activation [1]. Blood samples were drawn at baseline, 2 h, 4 h and 24 h. Immune cell phenotypes were examined with flow cytometry. In this data article the expression strength of markers involved in immune activation and immunosuppression as well as maturation, migration, cell death and responsiveness to signalling on monocyte and cDC subsets, as well as NK cells, CD4+ and CD8+ cells and regulatory T cells (Treg) are presented. These data improve our understanding of the immunomodulatory effects of the glucocorticoid dexamethasone , which may be important for the optimisation of treatment regimens as well as the evaluation of new indications for glucocorticoid treatment.in vivo