Parental care (PC) is rare in squamate reptiles and few studies have identified the benefits selecting for this form of grouping behavior in nature. We conducted a multiyear investigation of Liolaemus multicolor, a high Andean viviparous lizard that exhibits putative PC in the form of long-term associations between adult females and neonates. We studied these lizards at Nevado de Acay, Salta, Argentina (~4300 m) by (1) employing mark–recapture and focal animal observations to quantify the rate and duration of female–neonate associations in nature; (2) conducting a kinship analysis of ~500 SNPs to determine whether females grouping with neonates were their mothers; and (3) introducing conspecifics to focal females with and without neonates to assess differences in aggression and whether females defended associated neonates in nature. Our investigation revealed (1) females formed stable associations with 1–4 neonates for up to 4 mo; (2) most (84%) of our female–neonate focal groups (n = 13) represented mother–offspring associations; and (3) females with neonates were more aggressive towards conspecifics, particularly adult males, than unassociated females. These results support our hypothesis that long-term mother–offspring associations in L. multicolor likely confer fitness advantages by improving neonate survival in the harsh environment of the Argentine Puna. Future studies will compare the long-term survival of orphaned and mother-associated neonates.