We compute the asymptotics of the determinants of certain n×n Toeplitz + Hankel matrices T n (a) + H n (b) as n → ∞ with symbols of Fisher-Hartwig type. More specifically we consider the case where a has zeros and poles and where b is related to a in specific ways. Previous results of Deift, Its and Krasovsky dealt with the case where a is even. We are generalizing this in a mild way to certain non-even symbols.E if a is a sufficiently well-behaved function. Such a result is an analogue of the classical Szegö-Widom limit theorem [17] for Toeplitz determinants.The above determinant is a special case of more general determinants, det (a j−k + b j+k+1 ) j,k=0,...,n−1,