Borderline personality disorder (BPD) is associated with perinatal depression and parenting difficulties. However, little is known about the characteristics and specific effects of BPD in women with postpartum depression. This study aimed to explore 1) the sociodemographic, mental health characteristics, and motherhood difficulties in women with a major depressive postpartum episode (MDPE) and a comorbid diagnosis of BPD, compared to those with other personality disorders (other PD) or no PD and 2) whether BPD itself may be an independent risk factor for infant neglect in women with a MDPE. 412 women admitted to a Mother and Baby Unit (2001–2010) with a MDPE were involved in this study. Our study showed that women with MDPE-BPD (n = 64) more frequently reported a history of childhood maltreatment, single status, low social support, a history of depression, smoking during pregnancy and suicide attempt during the perinatal period compared to women with other PDs (n = 88) or no PD (n = 260). Women with comorbid BPD had a greater length of stay. Regarding infant care, neglect, abuse, and separation at discharge were more frequent in women with comorbid BPD. Logistic regression was performed to specifically examine whether BPD in women with a MDPE was an independent risk factor for infant neglect during the postpartum period. Comorbid BPD was independently associated with infant neglect (OR = 2.21; CI95% [1.02–4.81]). Our results underline the importance of screening for BPD in women with perinatal depression. Further studies are needed to explore the links between MDPE, BPD, and infant development. © 2021Read less <