  McLean proved that the moduli space of coassociative deformations of a
compact coassociative 4-submanifold C in a G_2-manifold (M,phi,g) is a smooth
manifold of dimension equal to b^2_+(C). In this paper, we show that the moduli
space of coassociative deformations of a noncompact, asymptotically cylindrical
coassociative 4-fold C in an asymptotically cylindrical G_2-manifold (M,phi,g)
is also a smooth manifold. Its dimension is the dimension of the positive
subspace of the image of H^2_cs(C,R) in H^2(C,R).
