Maternal separation anxiety (MSA) refers to feelings of anxiety elicited in a mother during separation from her infant. The role of social and structural disadvantage in the etiology of high MSA has been overlooked. Secondary analysis of data from the Longitudinal Study of Australian Children (N = 3,897) revealed that compared to socioeconomically advantaged women, women of low socioeconomic position had a fourfold increased odds of reporting high (>80th percentile) MSA (odds ratio = 4.37, 95% confidence interval = 3.24-5.89), even when maternal and infant characteristics were controlled for. Inadequate social support and residing in a poor quality neighborhood were also significantly associated with high MSA in adjusted analyses. These findings indicate that high MSA is more common in socioeconomically disadvantaged women and might be a response to adverse circumstances. Mothers’ experience of, and reasons for, MSA needs to be considered in policy formulation about parental leave and postpartum employment, particularly for disadvantaged mothers.