The pseudo-unitary group U (p, q) of signature (p, q) is the group of matrices that preserve the indefinite pseudo-Euclidean metric on the vector space C p,q . The goal of this paper is to describe the set Us (p, p) of Hermitian, or, self-adjoint elements in U (p, p).Mathematics Subject Classification (2010): 15B57, 15Axx, 20G20.