This paper presents a method of mistuning identification for turbomachinery blisks (integrally bladed disks) from measurements of the system modes and natural frequencies. The procedure is based on the "Best Achievable Eigenvectors" of all measured modes simultaneously combined with a regulation technique. Four illustrative numerical simulations, based on a reduced-order model of the blisk, are given which demonstrate that this technique produces acceptable mistuning identification. To do so, a finite element model of the bladed disk and a computational reduced-order modelling technique, based on component-mode substitution method and combined with a cyclic characteristic of the blade assembly, are developed. Moreover, sensibility coefficients of the mistuning parameter with respect to measured data are derived.