Expanded newborn screening (NBS) for genetic disorders has improved diagnosis of numerous treatable diseases, positively impacting children's health outcomes. However, research about the psychological impact of expanded NBS on families, especially mothers, has been mixed. Our study examined associations between maternal experiences of expanded NBS and subsequent psychosocial functioning and parenting stress in mothers whose infants received either true negative (TN), true positive (TP) or false positive (FP) results after a 4- to 6-month period. The Parenting Stress Index and the Depression, Anxiety and Stress Scale were used to assess symptoms of anxiety, stress and depression in 3 sets of mothers, whose infants received TN (n = 31), TP (n = 8) or FP (n = 18) results. Multivariate analyses of variance (MANOVA) results revealed no significant differences among these three groups of mothers regarding overall anxiety, stress and depression. However, FP mothers experienced lower levels of stress related to their own health compared to TN group. Two potential trends were also identified; results suggested TN mothers might experience higher levels of isolation than mothers in the TP group and that FP mothers might report higher stress levels in relation to spousal relationships compared to the TN group. FP mothers seemed to report similar or better levels of psychosocial functioning than TN mothers. Our findings are encouraging with respect to impacts of NBS on maternal well-being. We also identify key areas for improvement (parental education) and research (isolation and spousal relationships).