The problem of robust stability and performance in feedback control systems with n real (possibly repeated) uncertain parameters and structured unmodelled dynamics, the latter taking the form ofmcomplex blocks dynamic uncertainties is considered. A robustness marginrmis defined with respect to such model uncertainty structure and an algorithm is developed to compute it. Robust stability and performance is characterized in terms ofrmin much the same way as with the Multivariate Stability Marginkmor the Structured Singular value μ. An iterative procedure employing the above algorithm is given to compute tight bounds onkmand μ. These bounds are exact for the case m ≤ 3.