About 1-2/1000 of postpartum women require psychiatric admission. Length of stay is variable, and little is known about short postpartum admission. From all women in Ontario, Canada, with a psychiatric admission within 1 year postpartum (2007-2012) (n = 1702), we compared women with admissions <72 h to women with longer admissions on sociodemographics, clinical characteristics and post-discharge mental health service use. About 37% of admissions were <72 h. These women were more likely to be adolescents (11.7 vs 7.3%), less likely to be employed (16.6 vs 25.9%) compared to women with longer admissions, and fewer had a prior history of psychiatric admission (16.7 vs 59.0%). Index diagnoses of alcohol or substance use (12.5 vs 7.8%) and adjustment disorders (15.8 vs 6.3%) were more common in the short vs longer stay group; psychotic (5.8 vs 19.5%) and bipolar disorders (2.1 vs 14.2%) were less common. Women with short admission were at higher crude risk for ED revisit 7 days post-discharge (11.4 vs 4.9% OR2.52, 95% CI1.74-3.66) and at lower adjusted risk for readmission at 365 days post-discharge (19.5 vs 28.8%, aOR 0.63, 95% CI 0.46-0.85). Women with short stay postpartum admissions are a clinically distinct group that may benefit from targeted intervention.