Psoriasis is a chronic disease, the severity of which varies among patients and changes unpredictably over time in individual patients. Psoriasis can be exacerbated during treatment by infection, endocrine factors, hypocalcemia, medications, psychologic stress, skin trauma, or other factors. Patients who discontinue treatments may experience a return of disease--relapse--or worsening of disease--rebound. The National Psoriasis Foundation (NPF) proposed standardized definitions of relapse and rebound. Efalizumab, a recombinant humanized immunoglobulin G-1 monoclonal antibody, is approved for the management of psoriasis. During efalizumab clinical trials, a small percentage of patients experienced protocol-defined adverse events related to psoriasis. After publication of the NPF definition of rebound, post hoc exploratory analyses of the efalizumab clinical trial data were performed. The efalizumab clinical trial investigators discussed their observations, the analyses, and their individual approaches to the treatment of patients receiving or discontinuing efalizumab therapy, the conclusions of which are described herein.