Dermatomyositis and polymyositis patients have an increased risk of developing cancers. We have assessed the diagnostic values of serum tumor markers for the detection of solid cancer in dermatomyositis/polymyositis patients. Serum carcinoembryonic antigen, CA15-3, CA19-9, and CA125 were assayed by immunoradiometric methods in 102 dermatomyositis/polymyositis patients. All the patients had complete physical examination, chest X-ray, echocardiogram, gastrointestinal tract endoscopic explorations, thoracoabdomino-pelvic computed tomography scan, and all women had gynecologic examination and mammogram. Exclusion criteria for study were childhood dermatomyositis, inclusion body myositis, myositis associated with a connective tissue disease, prior history of cancer, and the presence of benign conditions known to elevate serum tumor markers. After a median follow-up of 59 months, 10 (9.8%) patients had a solid cancer. Initial elevation of CA125 was associated with an increased risk of developing solid cancer [P = 0.0001 by Fisher's exact test; odds ratio (OR), 29.7; 95% confidence interval (95% CI), 8.2-106.6]. For CA19-9, there was a trend towards a significant association (P = 00.7; OR, 4.5; 95% CI, 1-18.7, respectively). Diagnostic values of elevated CA125 and CA19-9 at screening increased when the study analysis was restricted to patients who developed a cancer within 1 year (P < 0.0001 and P = 0.018, respectively) or to patients without interstitial lung disease (P = 0.00001; OR, 133; 95% CI, 6.5-2733 and P = 0.027; OR, 9; 95% CI, 1.5-53, respectively). Individual comparisons of the baseline and the second CA125 value showed that three of the eight patients with cancers versus 3 of the 76 patients without, displayed an increase of their CA125 level (P = 0.01 by Fisher's exact test). We conclude that CA125 and CA19-9 assessment could be useful markers of the risk of developing tumors for patients with dermatomyositis and polymyositis and should therefore be included in the search for cancer in dermatomyositis/polymyositis patients, especially for patients without interstitial lung disease.