Lactogenesis II is the onset of copious milk production (i.e., the milk “coming in”), which usually occurs between 30 to 40 hours postpartum. When lactogenesis II fails to occur or is delayed, it may be due to a number of underlying hormonal or non-hormonal conditions. Of the various hormonal etiologies, many can be identified with the aid of a few standard blood tests. Gestational ovarian theca lutein cysts may cause delayed lactogenesis II and are fairly easily detected by ordering testosterone levels. Although this condition can delay lactogenesis II for as long as 31 days, with proper management women affected by these cysts have established breastfeeding. Three of the four women reviewed in this article were eventually able to produce 100% of their infants'caloric requirements.