This is an open-label, multicenter study designed to evaluate the efficacy and safety of efalizumab administered at weekly SC (subcutaneous) doses of 1.0 mg/kg followed by efalizumab taper in subjects with plaque psoriasis who previously participated in Study ACD2390g.

Inclusion Criteria:

• Signed informed consent
• Previous participation in Study ACD2390g
• For women of childbearing potential, continued use of an acceptable method of contraception for the duration of their participation in the study
• Willingness to continue to hold sun exposure reasonably constant and to avoid use of tanning booths or other UV light sources throughout the study

Exclusion Criteria:

• Any medical condition that, in the judgment of the investigator, would jeopardize the subject's safety following exposure to efalizumab
• Systemic therapy for psoriasis (ET Day 0 through FU Day 84 or upon relapse or unusual presentation of psoriasis in the FU period, whichever occurs first)
• Systemic immunosuppressive drugs for other indications (ET Day 0 through FU Day 84)
• Topical therapies for psoriasis (ET Day 0 through ET Day 84)
• Live virus or bacteria vaccines (ET Day 0 through FU Day 84)
• Other vaccines or allergy desensitization (it is recommended that these be scheduled after FU Day 84)
• Other experimental drugs or treatments (ET Day 0 through FU Day 84)
• Beta-Blockers, ACE inhibitors, interferons, quinidine, antimalarial drugs, or lithium (if clinically indicated, such medications are allowed but the dosage should be held constant between ET Day 0 and TT Day 84)