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Objective Idiopathic inflammatory myositis-associated interstitial lung disease (IIM-ILD) significantly increases morbidity and mortality. Lung ultrasound B-lines and Krebs von den Lungen-6 (KL-6) are identified as new sonographic and serum markers of ILD, respectively. The aim of our work was to assess the role of B-lines and KL-6 as markers of the severity of IIM-ILD. For this purpose, the correlation among B-lines score, serum KL-6 levels, high-resolution CT (HRCT) score, and pulmonary function tests were investigated in IIM-ILD patients. Methods Thirty-eight patients with IIM-ILD underwent chest HRCT scans, lung ultrasound and pulmonary function tests (independently performed within 1 week) examination. To assess severity and extent of ILD at HRCT, the Warrick score was used. The B-lines score denoting the extension of ILD was calculated by summing the number of B-lines on a total of 50 scanning sites. Serum KL-6 levels (U/ml) was measured by chemiluminescent enzyme immunoassay. Results A significant correlation was found between the B-lines score and serum KL-6 levels (r  = 0.43, P  < 0.01), and between the Warrick score and serum KL-6 levels (r  = 0.45, P  < 0.01). A positive correlation between B-lines score and the Warrick score (r  = 0.87, P  < 0.0001) was also confirmed. Both B-lines score and KL-6 levels inversely correlated to diffusion capacity for carbon monoxide (r  = −0.77, P  < 0.0001 and r  = −0.42, P  < 0.05, respectively) and total lung capacity (r  = −0.73, P  < 0.0001 and r  = −0.36, P  < 0.05, respectively). Moreover, B-lines correlated inversely with forced vital capacity (r  = −0.73, P  < 0.0001), forced expiratory volume in 1 s (r  = −0.69, P  < 0.0001). Conclusion B-lines score and serum KL-6 levels correlate with HRCT findings and pulmonary function tests, supporting their use as measures of IIM-ILD severity. [ABSTRACT FROM AUTHOR]