Postpartum depression (PPD) is a common complication following delivery, though evidence-based treatment options are limited. This study explores the feasibility and efficacy of outpatient PPD treatment with transdermal estradiol (TE). In a pilot, double-blind, placebo-controlled trial, women with PPD were randomized to receive transdermal 17β-estradiol (100mcg/day) or placebo patch. Over 6weeks, women completed weekly ratings on the Beck Depression Inventory (BDI), Edinburgh Postnatal Depression Scale (EPDS), and Hamilton Depression Scale (HAM-D). Primary outcome measures were treatment response (> 50% decrease from baseline BDI) and remission (BDI < 10) at 6weeks, and secondary outcome measures included severity on all scales at weeks 3 and 6. Of 12 recruited women, 6 received TE and 6 received placebo. By week 6, 5 women receiving TE responded to treatment and 4 showed symptom remission, compared to 2 responders and 1 remitter in the placebo group. This difference was not significant (p = 0.24). In a mixed-model of BDI ratings, TE was associated with a 9.2 point decrease at 3weeks (95%CI - 19.5 to + 1.0, p = 0.074) and a 10.5 point decrease at 6weeks (95%CI - 21.0-0.0, p = 0.049) compared to placebo, though these differences did not survive multiple comparisons correction. Analogous effects were found for HAM-D but not EPDS scores. Interestingly, no significant difference in plasma estradiol levels existed between groups. We were unable to demonstrate a significant therapeutic benefit of TE compared with placebo in PPD. Although limited by under-recruitment and loss to follow-up, our results suggest TE is a feasible option for outpatient PPD management, with preliminary evidence (based on secondary outcomes) for efficacy. Therapeutic effects may be seen as early as 3weeks and may not directly depend on peripheral measures of estradiol.