We present the case of a female, aged 22 years, with a long history of recalcitrant pustular psoriasis and psoriatic arthritis, treated with ustekinumab during pregnancy. The result of treatment was an uncomplicated pregnancy with delivery, at term, of a healthy boy. To our knowledge, this is the first reported use of ustekinumab in a human during pregnancy. Following a description of the case, we discuss the characteristics of ustekinumab and review the known information from human case reports, case series, and animal studies regarding the use of TNF-a inhibitors and ustekinumab during pregnancy. We also provide a short discussion of administration of ustekinumab during the time period when a mother is nursing and the potential for complications to infants in this setting.