Waveguide structures are fabricated in z-cut lithium niobate (LiNbO 3) using focussed femtosecond pulses. Two different types of waveguide structure are fabricated depending on the pulse energy used. In the first, guiding occurs in regions directly surrounding a visible laser-damage region. In the second, guiding occurs in a material modification region created at the focus. High confinement guiding at 1550 nm is demonstrated in the first type of waveguide but found to be temporary, thus indicating that at least part of the refractive index change is due to phenomena such as stress that are subject to relaxation. Finally, the polarization dependent guiding properties of the structures are investigated. © 2006 American Institute of Physics.