Approximations for structural response and design sensitivities signie cantly reduce the computational cost of structural optimization. To be useful, the approximation must be accurate and computationally efe cient. Damage tolerant design puts even more stringent computational demands on optimization procedures and approximations duetothelargestructuralchangesinherentindamage.Arobustapproximationisevaluatedandextendedtoinclude design sensitivities. It is implemented in an optimization procedure and tested. It is shown that this approximation is accurate and efe cient for damage tolerant optimum design of complex structural models. Last, a qualitative measure is developed and tested that estimates the computational savings using these approximations.