Let R be a ring. An additive mapping F : R → R is called a generalized derivation if there exists a derivation d of R such that F(xy) = F(x)y + xd(y) for all x, y ∈ R. The main purpose of this paper is to characterize some specific classes of generalized derivations of rings. Precisely, we describe the structure of generalized derivations of noncommutative prime rings with involution that belong to a particular class of generalized derivations. Consequently, some recent results in this line of investigation have been extended. Moreover, some suitable examples showing that the assumed hypotheses are crucial, are also given.