Based on the Berger-Simons holonomy classification, we characterize al
l Riemannian spin manifolds carrying a twister spinor with at least on
e zero. In particular, the dimension n of the manifold is either even
or n = 7, Outside the set of zeros of the twister spinor the metric is
conformal to either a flat metric or a Ricci flat and locally irreduc
ible metric.