  We generalize certain parts of the theory of group rings to the twisted case.
Let G be a finite group acting (possibly trivially) on a field L of
characteristic coprime to the order of the kernel of this operation. Let K in L
be the fixed field of this operation, let S be a discrete valuation ring with
field of fractions K, maximal ideal generated by pi and integral closure T in
L. We compute the colength of the twisted group ring T G in a maximal order in
L G. Moreover, if S/pi S is finite, we compute the S/pi S- dimension of the
center of T G/Jac(T G). If this quotient is split semisimple, this yields a
formula for the number of simple T G-modules, generalizing Brauer's formula.
