Tumor necrosis factor–alfa levels are linked to disease severity in patients with inflammatory conditions, such as psoriasis. Inhibitors of this cytokine are commonly used with significant success in the treatment of such inflammatory disorders. Their use, however, can be plagued by infectious complications. An awareness of potential infections associated with these therapies is critical in order to maximize preventive efforts both before and during therapy. This review provides a guide for dermatologists caring for patients in need of this type of biologic therapy to preemptively address the infectious risks. Part I of this continuing medical education article reviews background information on the various infectious risks associated with tumor necrosis factor inhibitor therapy and appropriate historical data to obtain in the context of pretherapy evaluations.