T cell-specific adapter protein (TSAd) encoded by the SH2D2A gene is expressed in activated T cells, NK cells and endothelial cells, but its tissue expression has not yet been mapped. Here, we have defined the specificity of two commercially available anti-TSAd monoclonal reagents using peptide arrays. We found them to bind separate epitopes in the C-terminal part of TSAd. We then used immunohistochemistry to examine TSAd expression in various human lymphoid and non-lymphoid tissues. Immunostaining of adjacent tissue sections revealed that a substantial fraction of CD3-positive cells in normal lymphoid and non-lymphoid tissues expressed TSAd. In particular, essentially all intra-epithelial T cells appeared to coexpress TSAd. In addition, TSAd expression was observed in endothelial cells of dermal microvessels, while it was not detected in endothelial cells of the other tested tissues. This work provides insight into the expression pattern of TSAd in various healthy human tissues.