Maternal behavior in the new mother is a multidimensional set of responses to infant cues that are influenced by the mother's early life experiences. In this study, we wanted to test if mothers' early life experiences and mothers' genotype have interactive effects on maternal behaviors and attitudes, something which has not been previously explored. In a sample of 204 mothers, we assessed maternal genotype at the serotonin transporter-linked polymorphic region (5-HTTLPR) and an adjacent upstream polymorphism (rs25531), together giving rise to three alleles: short (S), LG and LA. Controlling for maternal age and parity, we showed that this genotype can predict differences in maternal sensitivity at 6 months postpartum: mothers with an S (or the functionally similar LG) allele were more sensitive than mothers who lacked the allele during a 30-min recorded mother–infant interaction (F (4,140) = 3.43; P = 0.01). Furthermore, we found highly significant gene–environment interactions in association with maternal behavior, such that mothers with no S or LG alleles oriented away more frequently from their babies if they also reported more negative early care quality (F (5,138) = 3.28; P = 0.008). Finally, we found significant gene–environment associations with maternal attitudes; mothers with the S allele and with greater early care quality scored higher on ratings of their perceived attachment to their baby (F (5,125) = 3.27; P = 0.008).