Inclusion Criteria:
* Male or female patients. Women of childbearing potential\* must be ready and able to use highly effective methods of birth control per International Council on Harmonisation (ICH) M3(R2) that result in a low failure rate of less than 1% per year when used consistently and correctly. A list of contraception methods meeting these criteria is provided in the patient information.
\*Women of childbearing potential are defined as:
* having experienced menarche and are
* not postmenopausal (12 months with no menses without an alternative medical cause) and are
* not permanently sterilized (e.g., tubal occlusion, hysterectomy, bilateral oophorectomy or bilateral salpingectomy).
* Age ≥ 18 years at screening
* Have a diagnosis of chronic plaque psoriasis (with or without psoriatic arthritis) for at least 6 months before the first administration of study drug.Duration of diagnosis may be reported by the patient,
* Have stable moderate to severe chronic plaque psoriasis with or without psoriatic arthritis at both Screening and Baseline (Randomization):
1. Have an involved body surface area (BSA) ≥ 10% and
2. Have a Psoriasis Area and Severity Index (PASI) score ≥ 12 and
3. Have a static Physician Global Assessment (sPGA) score of ≥ 3.
* Must be candidates for systemic therapy or phototherapy for psoriasis treatment, as assessed by the investigator
* Must be a candidate for treatment with Stelara® (ustekinumab) according to local label.
* Signed and dated written informed consent prior to admission to the study in accordance with Good Clinical Practices (GCP) and local legislation
Exclusion Criteria:
* Patients with:
1. non-plaque forms of psoriasis (including guttate, erythrodermic, or pustular),
2. current drug-induced psoriasis (including an exacerbation of psoriasis from beta blockers, calcium channel blockers, or lithium),
3. active ongoing inflammatory diseases other than psoriasis and psoriatic arthritis that might confound trial evaluations according to investigator's judgment,
* Previous exposure to BI 655066,
* Currently enrolled in another investigational study or less than 30 days (from screening) since completing another investigational study (participation in observational studies is permitted),
* Previous exposure to ustekinumab (Stelara®),
* Use of any restricted medication, or any drug considered likely to interfere with the safe conduct of the study,
* Major surgery performed within 12 weeks prior to randomization or planned within 12 months after screening (e.g., hip replacement, aneurysm removal, stomach ligation),
* Known chronic or relevant acute infections including active tuberculosis, HIV or viral hepatitis; QuantiFERON® tuberculosis (TB) test or purified protein derivative (PPD) skin test will be performed according to local labelling for comparator products. If the result is positive, patients may participate in the study if further work up (according to local practice/guidelines) establishes conclusively that the patient has no evidence of active tuberculosis. If presence of latent tuberculosis is established, then treatment should have been initiated and maintained according to local country guidelines,
* Any documented active or suspected malignancy or history of malignancy within 5 years prior to screening, except appropriately treated basal or squamous cell carcinoma of the skin or in situ carcinoma of uterine cervix,
* Evidence of a current or previous disease, medical condition (including chronic alcohol or drug abuse) other than psoriasis, surgical procedure (i.e., organ transplant), medical examination finding (including vital signs and electrocardiogram \[ECG\]), or laboratory value at the screening visit outside the reference range that is in the opinion of the investigator, is clinically significant and would make the study participant unreliable to adhere to the protocol or to complete the trial, compromise the safety of the patient, or compromise the quality of the data,
* History of allergy/hypersensitivity to a systemically administered biologic agent or its excipients,
* Women who is pregnant, nursing, or who plans to become pregnant while in the trial,
* Previous enrolment in this trial.
