We experimentally investigated the relative role of kinship and density on juvenile dispersal in the common lizard. A few days after birth, juveniles were introduced into seminatural endosures, where they experienced different social environments in the first experiment we varied the density of unrelated adults (males or females) within the enclosure (0, 1, or 2 adults), and in the second experiment, we varied the level of kinship and familiarity between juveniles and adults. Each enclosure was connected to a second enclosure by small holes which allowed only juveniles to move between enclosures. Juvenile movements were monitored during 14 days after birth, as juvenile dispersal is mainly completed within 10 days after birth under natural conditions. Most juveniles did not return to the first enclosure. Sex had no effect on juvenile dispersal. Adult densityand kinship with adults both affected dispersal. Adult female density increased juvenile dispersal whatever the level of kinship and familiarity with the females. Dispersers had better body condition than nondispersers at high female densit and this difference was significantly greater when the mother and the familiar female were present in the enclosure. Furthermore, body condition of mothers and familiar females was positively correlated with juvenile dispersal, whereas there was no such correlation in the case of unfamiliar and unrelated females. These results strongly suggest that adult female density is a major factor promoting dispersal in this species and that both intraspecific and kin competition motivate dispersal.