Reports of postpartum parental care in squamate reptiles (lizards and snakes) are rare and generally anecdotal. We investigated parental care in black rock skinks, Egernia saxatilis, from southeastern Australia. These lizards live in small family groups, with adults defending territories against conspecifics. Juvenile lizards live within their parents' territory and may thus be protected from infanticide. In staged encounters in the laboratory, adults frequently attacked unrelated juveniles but not their own offspring, and the parent's presence significantly reduced the incidence of this infanticidal aggression. This protection arose not through specific 'parental' behaviours, but because adults tended to ignore juveniles when another (potentially threatening) adult was present. When two family groups were placed in the same enclosure, one family rapidly became dominant over the other. Juveniles of the dominant family derived thermoregulatory and foraging benefits from their parents' status. Thus, some lizards do show postpartum parental care, and may thereby significantly benefit their progeny via reduced risk of infanticide and better access to thermal and nutritional resources.