  Neutralino dark matter in supersymmetric models is revisited in the presence
of flavor violation in the soft supersymmetry breaking sector. We focus on
flavor violation in the sleptonic sector and study the implications for the
co-annihilation regions. Flavor violation is introduced by a single
$\tilde{\mu}_R-\tilde{\tau}_R$ insertion in the slepton mass matrix. Limits on
this insertion from BR($\tau \to \mu + \gamma$) are weak in some regions of the
parameter space where cancellations happen within the amplitudes. We look for
overlaps in parameter space where both the co-annihilation condition as well as
the cancellations within the amplitudes occur. In mSUGRA, such overlap regions
are not existent, whereas they are present in models with non-universal Higgs
boundary conditions (NUHM). The effect of flavor violation is two fold: (a) it
shifts the co-annihilation regions towards lighter neutralino masses (b) the
co-annihilation cross sections would be modified with the inclusion of flavor
violating diagrams which can contribute significantly. Even if flavor violation
is within the presently allowed limits, this is sufficient to modify the
thermally averaged cross-sections by about (10-15)% in mSUGRA and (20-30)% in
NUHM, depending on the parameter space. In the overlap regions, the flavor
violating cross sections become comparable and in some cases even dominant to
the flavor conserving ones. A comparative study of the channels is presented
for mSUGRA and NUHM cases.
