Background: Etanercept is a tumour necrosis factor antagonist that is approved in the U.S.A., Canada and Europe for treating adult patients with chronic moderate to severe plaque psoriasis. Objectives: To assess whether clinical efficacy, safety and pharmacokinetic (PK) profiles of etanercept 50 mg once weekly are comparable to etanercept 25 mg twice weekly. Methods: Patients from a U.S. phase 3 study and a global phase 3 study were subsequently enrolled in an open-label extension study (extension study) where they all received etanercept at a dose of 50 mg once weekly for an initial 12 weeks. Patients who had received at least 24 weeks of etanercept 25 mg twice weekly in the global phase 3 study and were enrolled in the extension study (n = 265) were assessed for efficacy and safety at extension study baseline and after 12 weeks of etanercept 50 mg once weekly. Efficacy endpoints included the Psoriasis Area and Severity Index (PASI), the Dermatology Life Quality Index and the Physician's Global Assessment of psoriasis. In addition, PK profiles from patients in the U.S. phase 3 study were compared with PK profiles from another set of patients in the extension study. Comparison was made between a subset of patients receiving etanercept 25 mg twice weekly dosing in the U.S. phase 3 study (n = 13) and those receiving etanercept 50 mg once weekly in the extension study (n = 84). Results: The mean PASI score was 5.77 at extension study baseline after treatment with etanercept 25 mg twice weekly, which was sustained at 5.82 after 12 weeks of etanercept 50 mg once weekly. Similar results were observed in other efficacy endpoints. Etanercept 50 mg once weekly was generally well tolerated. No new safety findings were reported. PK profiles overlapped extensively between the two dosing regimens. Conclusions: In this report, we demonstrate that efficacy, safety and PK profiles were comparable between etanercept 25 mg twice weekly and 50 mg once weekly in patients who had received at least 24 weeks of etanercept 25 mg twice weekly prior to receiving etanercept 50 mg once weekly in the extension study. © 2007 British Association of Dermatologists.