We present a comparison of the lithium abundances of stars with and without planetary-mass companions. New lithium abundances are reported in 79 planet hosts and 38 stars from a comparison sample. When the Li abundances of planet host stars are compared with the 157 stars in the sample of field stars of Chen et al. (cite{Chen2001}) we find that the Li abundance distribution is significantly different, and that there is a possible excess of Li depletion in planet host stars with effective temperatures in the range 5600-5850 K, whereas we find no significant differences in the temperature range 5850-6350 K. We have searched for statistically significant correlations between the Li abundance of parent stars and various parameters of the planetary companions. We do not find any strong correlation, although there are may be a hint of a possible gap in the Li distribution of massive planet host stars. Based on observations collected at the La Silla Observatory, ESO (Chile), with the CORALIE spectrograph at the 1.2 m Euler Swiss telescope, and with the FEROS spectrograph at the 1.52 m ESO telescope, and using the UES spectrograph at the 4.2 m William Herschel Telescope (WHT) and SARG spectrograph at the 3.5 m Telescopio Nazional Galileo on La Palma (Canary Islands).