['To determine whether IL-18 is involved in the inflammation of DM and PM.', 'Thirty-three patients with DM were enrolled in this study, including 25 with interstitial lung disease (ILD). In addition, 16 patients with PM were enrolled, including 6 with ILD. All patients were admitted to our hospital as a result of their condition requiring treatment, and clinical laboratory data including serum IL-18 were recorded on admission.', 'Serum IL-18 was significantly (P\u2009<\u20090.0001) higher in both DM and PM patients than in healthy controls (n\u2009=\u200930). Serum ferritin and IL-18 were significantly (P\u2009=\u20090.003 and 0.0044, respectively) higher in DM than in PM patients. Additionally, ferritin and IL-18 were significantly (P\u2009=\u20090.023 and 0.034, respectively) higher in DM patients with ILD than in DM patients without ILD. Significant positive correlations were found between creatine kinase (CK) and ferritin (r(s)\u2009=\u20090.39, P\u2009=\u20090.024); CK and IL-18 (r(s)\u2009=\u20090.48, P\u2009=\u20090.005); and IL-18 and ferritin (r(s)\u2009=\u20090.54, P\u2009=\u20090.0012) in the DM group as a whole. These findings were different for the DM plus ILD subgroup: significant positive correlations were found between CK and ferritin (r(s)\u2009=\u20090.40, P\u2009=\u20090.047); CK and IL-18 (r(s)\u2009=\u20090.63, P\u2009=\u20090.0008); and IL-18 and ferritin (r(s)\u2009=\u20090.41, P\u2009=\u20090.042).'] Is interleukin-18 a key mediator in dermatomyositis : potential contribution to development of interstitial lung disease?