Objectives To analyze the diagnostic utility of lung ultrasound (US) to detect interstitial lung disease (ILD) in rheumatoid arthritis (RA) patients comparing with high-resolution computed tomography (HRCT) Patients and methods We performed a cross-sectional, observational study in patients with RA-ILD (cases) controlled with a group of RA patients without ILD (controls) paired by sex, age, and time of disease evolution. Patients were assessed using HRCT, PFT, and US. The main variables were B-line number, evaluation of the lung-US score already described, pleural irregularities, and A pattern US lost. ROC curve analysis was performed to establish the cut-off point of the US B-lines number for detecting the presence of significant RA–ILD in relation to HRCT, and logistic regression analysis was performed to identify the intercostal spaces. Results Seventy-one patients were included, 35 (49.2%) with ILD-RA and 36 (50.8%) RA controls. Regarding US score, we found that the detection of 5.5 lines in a reduced score of 8 intercostal spaces had a sensitivity = 62.2%, specificity = 91.3%, PPV = 88.4%, and NPV = 69.5%. In multivariate analysis, the intercostal spaces which showed independent association with ILD were 3rd right anterior axillary space (OR IC 95% 19.0 1.3–27.5), 8th right posterior axillary space (OR IC 95% 0.04 0.0–0.6), 8th right subscapular space (OR IC 95% 16.5 1.8–45.5), 9th right paravertebral space (OR IC 95% 7.11 1.0–37.1), and 2nd left clavicular middle space (OR IC 95% 21.9 1.26–37.8). Conclusions Lung ultrasound could be a useful tool for ILD diagnosis associated with rheumatoid arthritis. A 8-space reduced score showed a similar total predictive capacity than 72-space score. Key Points • Lung ultrasound could be a useful tool for ILD diagnosis associated with rheumatoid arthritis. • The 72-space evaluation is highly sensitive, whereas a simplified score enables a more specific and faster diagnosis. • The number of B lines is correlated with DLCO, ACPA, inflammatory activity, and physical function.