We characterize affinely regular polygons in a real affine space as follows. Consider two polygons P and Q with the same number of vertices and a common side, P being an affine image of some (convex or nonconvex) regular polygon. Q is then an affine image of the same regular polygon if and only if the vectors between the corresponding vertices of P and Q are uniquely determined multiples of the vector between the vertices just after the common side.
