Introduction: The medical treatment of inflammatory rheumatic diseases has improved dramatically during the last decades primarily due to the introduction of biological disease modifying anti-rheumatic drugs (bDMARDs). However, bDMARD treatment failure occurs in 30-40% of patients due to lack of effectiveness or side effects. The tools to predict treatment outcomes in the individual patient are currently limited. The objective of the present study is to identify diagnostic, prognostic and predictive biomarkers, which can be used to 1) diagnose inflammatory rheumatic diseases early in the disease course with high specificity and sensitivity, 2) improve prognostication or 3) predict treatment effectiveness and tolerability for the individual patient. Methods and analysis: Observational and translational open cohort study with prospective collection of clinical data and biological materials in patients with inflammatory rheumatic diseases treated in routine care. Patients contribute one cross-sectional blood sample (i.e. whole blood, serum, EDTA-plasma and -buffy coat, and blood in PAXgene RNA tubes) and/or are enrolled for longitudinal follow-up upon start of new DMARD (blood sampling after 0/3/6/12/24/36/48/60 months' treatment). Demographics, disease characteristics, comorbidities and lifestyle factors are registered at inclusion; DMARD treatment and outcomes are collected repeatedly during follow-up. Currently (June 2017) \>5,000 samples from ≈3,000 patients have been collected. Data will be analysed using appropriate statistical analyses. Ethics and dissemination: The protocol is approved by the Danish Ethics Committee and The Danish Data Protection Agency. All participants give written informed consent. Biomarkers will be evaluated and published according to REMARK, STROBE and STARD guidelines. Results will be published in peer-reviewed medical journals and presented at international conferences.