Biological therapies used in psoriasis treatment pose a risk of reactivation of hepatitis B virus (HBV) infection. This risk occurs not only in patients with HB surface antigen (HBsAg) (+) but also in patients with past or occult HBV infection (with negative HBsAg, positive HB core antibodies (HBcAb), and positive HBV deoxyribonucleic acid [DNA]). Ustekinumab (UST) is a biologic agent acts by blocking the IL-12/23 pathway. Thus, hindering this response may lead to HBV reactivation. UST therapy is associated with mild HBV-r risk; however, there is insufficient data to confirm that hypothesis. Herein, we present observations on the safety of UST therapy in patients with psoriasis and serologically proved past HBV infection. One-hundred and six consecutive patients with moderate to severe psoriasis treated with biological therapy between May 2013 and January 2020 were retrospectively analyzed. Out of 106 patients, there were five who reported having past HBV. Those five patients