Objective.To assess the responsiveness and repeatability of volumetric power Doppler ultrasound (PDUS) evaluation of synovitis and bone erosions in rheumatoid arthritis (RA).Methods.Twenty-three patients with RA (19 women, mean age 52.7 ± 12.6 yrs, mean disease duration 10.1 ± 8.6 yrs) were prospectively enrolled. All patients were beginning therapy with rituximab because of disease activity despite therapy with synthetic disease-modifying antirheumatic drugs and tumor necrosis factor-blocking agents. Patients underwent clinical, laboratory, and volumetric PDUS examination at baseline, 6 months, and 12 months. Ten centers participated in the study. Four centers recruited the patients and performed the volumetric acquisitions of PDUS images, while the remaining 6 centers assessed the PDUS volumes, blinded to the identity of patients and date of the visits. The most symptomatic hand and foot were scored for B-mode synovitis, synovial PD signal, and bone erosions. The repeatability of the volumetric PDUS assessment was investigated.Results.An overall improvement in clinical and PDUS measurements was found at the followup assessments. The mean indexes for synovial PD signal and bone erosions and the number of sites with abnormalities decreased significantly throughout the followup (p < 0.05). The intraacquisition, intrareader reliability was excellent for all PDUS measurements (intraclass correlation coefficients > 0.9).Conclusion.The results of our pilot study suggest that volumetric PDUS can be responsive and repeatable in multicenter cohort studies of RA. This technique may minimize assessment biases and reduce acquisition variability in open-label and observational studies.