To examine the value of optical spectral transmission (OST) in detecting joint inflammation in patients with rheumatoid arthritis (RA) and to evaluate whether OST correlates with certain patient characteristics.OST measurements were performed in the metacarpophalangeal, proximal intraphalangeal and wrist joints of 168 RA patients and 114 controls. OST difference between the two groups was statistically examined and subsequently controlled for the effect of possible confounding factors. Diagnostic OST performance was tested by Receiver Operating Characteristics. Moreover, associations of OST with clinical and serological activity markers (patient group), joint ultrasound (US) (patient subgroup) and various anthropometric and epidemiologic parameters (patient and control group) were evaluated by Spearmann's test and a generalized linear statistical adjustment model.OST was significantly higher in the RA group than in the control group, even after adjustment for confounding factors [1.89; 95%CI(0.709-3.070), padj=0.002)]. Taking US as a reference, Area Under the Curve (AUC) for all 1,251 joints simultaneously was 0.67 (95%CI=0.631- 0.709). In the patient group, correlation and adjustment analyses showed associations of OST with various disease activity markers [DAS28 (rho=0.313), swollen joint counts (rho=0.361), CRP (rho=0.389); all, padj=0.001)], age (rho=0.276, p<0.001) and osteoarthritis (p=0.022). Moreover, OST associated with a power-Doppler- (rho=0.442; p=0.001) and a grey-scale- US-Score (rho=0.591; p<0.001). In both groups males had significantly higher OST values than females and OST associated moderately-weakly with Body-Mass-Index (rhopatients=0.316, rhocontrols=0.24) (all; p<0.001).RA patients showed higher OST values in comparison to controls. Moreover, OST associated with clinical, US and laboratory disease activity markers.