We examined whether locus of control (LOC) moderates the apparent relationship between perfectionism and postpartum depression (PPD). It was predicted that external LOC would moderate the relationship between self-oriented perfectionism and PPD, and socially prescribed perfectionism and PPD. A sample of 243 women completed an online self-report questionnaire assessing perfectionism, LOC, and PPD. Self-oriented and socially prescribed perfectionism were significantly associated with PPD. Increased personal loci of control (i.e., low external LOC and high internal LOC) moderated (strengthened) the relationship between perfectionism and PPD. LOC may be an important concept and one of the underlying factors at work in the perfectionism–PPD relationship. This outcome may be attributed to the self-directed nature of self-oriented perfectionists.