The purpose of this study was to determine whether there are any differences in the appearance of tongue-surface structure in different kinds of collagen diseases, because red tongue is well known to be a very important feature of suspected Sjögren's syndrome (Sjs). To clarify some features of the filiform papillae on the dorsal surfaces of the tongues of patients with speculated Sjs, we observed a total of 565 individuals with primary Sjs (n = 24, M/F = 0/24), secondary Sjs (n = 16, M/F = 1/15), possible Sjs (n = 96, M/F = 21/75), collagen diseases (CD) (n = 55, M/F = 15/40; 15 SSc, 10 SLE 10, two MCTD, six dermatomyositis, and 22 others), various cutaneous disorders (n = 324, M/F = 118/206), and healthy controls (HC) (n = 50, M/F = 32/18) by using a dermoscope. The average ages of the patients with Sjs, CD (non-Sjs), cutaneous disorders (non-Sjs/CD), and HC were 56.4 14.8, 55.1 116.4, 51.1 121.2, and 37.1 110.6 years of age, respectively. The filiform papillae were classified into four patterns by their structural characteristics: normal papillae (no abnormality with clear cornified tips) (pattern I, n = 162), slightly rounded papillae with unclear cornified tips (pattern II, n = 239), rounded papillae without cornified tips (pattern III, n = 86), and completely flattened papillae (pattern IV, n = 28). Their patterns were reversely related to the volume of salivary fluid (gum test) (P = 0.046) and the degree of furor coating of the tongue (P = 0.051). Pattern IV is predominant in definitive Sjs (primary and secondary Sjs) (n = 15; 53.6%) with positive anti-SS-A or -B antibody (n = 8) with a specificity of 53.6% and a sensitivity of 36.6%. The present dermoscopic finding that the completely flattened pattern (IV) is predominant in definite Sjs patients may indicate a useful marker for suspicion of Sjs.