Let (X,\(\Sigma\),m) be a complete \(\sigma\)-finite measure space, and let T be a \(\Sigma\)-measurable mapping in X such that \(m\circ T^{-1}\) is absolutely continuous with respect to m. The corresponding weighted composition operator W on \(L^ 2(X,\Sigma,m)\) generated by the weight function \(\phi\) is defined by \(Wf:=\phi f\circ T\). A measure theoretic characterization of hyponormality for such operators is given. This generalizes a result of \textit{D. Harrington} and \textit{R. Whitley} [J. Oper. Theory 11, 125-135 (1984; Zbl 0534.47017)], who considered the case of unweighted composition operators (i.e. \(\phi =1)\). An example illuminating the connection to isometries is given.