BACKGROUND: Immunosuppressive agents may increase the risk of infections with human alphaherpesviruses. METHODS: We included all adult patients with moderate to severe psoriasis who initiated methotrexate (MTX) or biologic agents in a retrospective cohort study. An episode of alphaherpesviruses infection was defined as filling a prescription for systemic acyclovir, valacyclovir, or famciclovir. Using nationwide registries, we determined the incidence, risk factors, 180-day hospital contacts, and 30-day mortality following infection. RESULTS: We included 7294 patients; 4978 (68%) received MTX, and 2316 (32%) biologic agents. The incidence rates (95% confidence intervals) of alphaherpesviruses were 23 (20-27), 26 (19-35), 17 (11-27), and 6.7 (1.3-21) per 1000 person-years of follow-up in patients on MTX, tumor necrosis factor alpha (TNF-α) inhibitors, interleukin 12/23 (IL-12/23) inhibitors, and interleukin 17 (IL-17) inhibitors, respectively. Males had an unadjusted hazard ratio (HR) of 0.47 (P < .001) for alphaherpesvirus infection. Patients on IL-17 inhibitors had an adjusted HR of 0.24 (P = .048) compared to TNF-α inhibitors. Within 180 days after infection, 13%, 7.5%, and <0.5% of patients on MTX, TNF-α inhibitors, and IL-12/23 or IL-17 inhibitors, respectively, had hospital contacts, and the 30-day mortality for all groups was <0.5%. CONCLUSIONS: The incidence and risk of alphaherpesvirus infections were comparable between patients on MTX and TNF-α inhibitors, whereas use of IL-17 inhibitors was associated with a lower risk.