Abstract Introduction Progression of arterial involvement is often observed in patients with Takayasu arteritis (TA) thought to be in remission. This reflects the failure of currently used biomarkers and activity criteria to detect smouldering inflammation occurring within arterial wall. Pentraxin-3 (PTX3) is a soluble pattern recognition receptor produced at sites of inflammation and could reveal systemic as well as localized inflammatory processes. We verified whether the blood concentrations of PTX3 and of C-reactive protein (CRP) in patients with Takayasu arteritis (TA) might reflect vascular wall involvement, as assessed by signal enhancement after contrast media administration, and the progression of arterial involvement. Methods A cross-sectional single-centre study was carried out on 42 patients with TA that comprised assessment of PTX3, of CRP and erythrocyte sedimentation velocity (ESR). In total, 20 healthy controls and 20 patients with Systemic Lupus Erythematous (SLE) served as controls. Vascular imaging was carried out by magnetic resonance angiography, doppler ultrasonography and computed tomography angiography. Results Patients with TA and SLE had higher plasmatic PTX3 and CRP concentrations than healthy controls ( P = 0.009 and 0.017, respectively). PTX3 levels did not correlate with those of CRP. Patients with active systemic TA had significantly higher concentrations of CRP but similar levels of PTX3 than patients with quiescent disease. In contrast, patients with vascular inflammation detectable at imaging had higher PTX3 concentrations ( P = 0.016) than those in which vessel inflammation was not evident, while CRP levels were similar. The concentration of PTX3 but not that of CRP was significantly higher in TA patients with worsening arterial lesions that were not receiving antagonists of tumor necrosis factor-α or interleukin-6. Conclusions Arterial inflammation and progression of vascular involvement influence plasma PTX3 levels in TA, while levels of CRP accurately reflect the burden of systemic inflammation. These results support the contention that PTX3 reflects different aspects of inflammation than CRP and might represent a biomarker of actual arteritis in TA.