  The delay in light travel time along the line of sight generates an
anisotropy in the power spectrum of 21cm brightness fluctuations from the epoch
of reionization. We show that when the fluctuations in the neutral hydrogen
fraction become non-linear at the later stages of reionization, the light-cone
anisotropy becomes of order unity on scales >50 comoving Mpc. During this
period the density fluctuations and the associated anisotropy generated by
peculiar velocities are negligible in comparison.
