Inclusion Criteria:
* Subject must have body surface area (BSA) ≥ 10% and a target fingernail Modified Nail Psoriasis Severity Index (mNAPSI) ≥ 8 at Week 0, OR BSA ≥ 5%, a target fingernail mNAPSI ≥ 8 and a total mNAPSI score of ≥ 20 at Week 0.
* Subject must have a Nail Psoriasis Physical Functioning Severity score of \> 3, OR a Nail Psoriasis Pain Numeric Rating Scale (NRS) score of \>3.
* Subjects must have a Physician's Global Assessment (PGA) of Fingernail Psoriasis and a PGA of Skin Psoriasis of at least moderate.
* Subject must have discontinued use of all systemic therapies for the treatment of psoriasis, or systemic therapies known to improve psoriasis for at least 4 weeks prior to Week 0, ustekinumab must have been discontinued at least 12 weeks prior to Week 0.
* Target fingernail must have mNAPSI score of ≥ 8.
* Adult subjects with clinical diagnosis of chronic plaque psoriasis (with disease duration of at least 6 months).
Exclusion Criteria:
* Prior adalimumab therapy.
* Diagnosis of other active skin diseases or skin infections (bacterial, fungal, or viral) that may interfere with evaluation of skin or fingernail psoriasis.
* Recent infection requiring treatment.
* Significant medical events or conditions that may put patients at risk for participation, including recent history of drug or alcohol abuse.
* Female subjects who are pregnant or breast-feeding or considering becoming pregnant during the study.
* History of cancer, except successfully treated skin cancer.
