Knowledge of natal dispersal and juvenile survival from parental independence until recruitment into breeding populations is an important aspect of population dynamics studies. Dispersal allows genetic connectivity and demographic compensation between neighbouring populations. These issues are particularly significant for species confined to mountaintops, as is the Rock Ptarmigan Lagopus muta in southern Europe. We studied natal dispersal and survival in juvenile Rock Ptarmigan in the French Alps and Pyrenees between 1999 and 2018 by radiotracking 113 young captured in September in two study areas. At both sites natal dispersal occurred in two discrete phases, in autumn (October-November) and in spring (late March-mid-May). Juvenile females dispersed twice as far as males in autumn at both sites but this difference decreased in spring and was not significant. Juveniles of both sexes dispersed further in the Pyrenees than in the Alps (males: 3.5 vs. 1.4km; females: 6.5 vs. 4.4km), a situation we attribute more to genetic differences between the two populations rather than to environmental factors. As to geographical barriers to dispersal, our radiotracking data along with extensive visual observations suggest that Rock Ptarmigan living in the Alps and the Pyrenees rarely fly across valleys 10-12km wide. For sexes and locations combined, the survival rate of juvenile Rock Ptarmigan during a ten-month period (September to June) was 0.636 (95%CI: 0.551-0.734). Long-distance dispersal tended to reduce the survival of birds during their first breeding attempt (April-June), a result that suggests a delayed effect of such dispersal.