Kin selection in larval amphibians is hypothesized to increase survival to metamorphosis. While kin selection may benefit amphibians with obligate metamorphosis, increased survival within sibships may exert fitness costs on facultatively paedomorphic species, such as increased competition among kin. Consequently, it is unclear whether such species should engage in kin selection. We investigated kin selection in a facultatively paedomorphic salamander, Ambystoma talpoideum, using laboratory behavioural trials and microcosm experiments. Individuals were most aggressive towards familiar siblings, and full-sibship groups incurred more injuries than mixed-sibship groups; however, familiar siblings ultimately exhibited higher survival. Thus, while short-term responses appeared to reflect the hypothesized costs of kin recognition, long-term patterns of survival did not support this hypothesis. The inconsistencies between results suggest that short-term studies may not capture ontogenetic variation in kin selection, and that long-term studies are needed to better test the hypothesized effects of kin selection on survival and metamorphosis.