Nailfold capillary microscopy patterns in 22 patients with mixed connective tissue disease (MCTD) were compared with those of 21 patients with systemic lupus erythematosus (SLE) and 30 patients with systemic sclerosis (scleroderma [SD]). Microvascular data were classified blindly as follows: normal, nonspecific abnormalities, SD pattern, and SLE pattern, with special attention to the presence of dystrophic, branched "bushy" capillary formations. Of the 22 patients with MCTD, 63.6% had an SD pattern, 22.7% had an SLE pattern, 13.6% had nonspecific abnormalities, and 72.7% had bushy capillary formations. Compared with SLE microangiopathy, MCTD microangiopathy exhibited significantly greater capillary loss (P less than 0.05), more frequent SD patterns (P less than 0.001), and more frequent bushy capillaries (P less than 0.001). Compared with SD patients, MCTD patients displayed less frequent SD patterns (P less than 0.02) and more frequent bushy capillary formations (P less than 0.01). The presence of bushy capillaries was suggestive of MCTD. For diagnostic purposes, bushy capillaries displayed 72% sensitivity, 80% specificity, and 87.2% negative predictive value. The quantitative and qualitative expressions of microangiopathy were different in MCTD and SLE, respectively. This supports the hypothesis that each disease is a distinct entity. Nevertheless, there were many resemblances between MCTD and SD, which implies that MCTD is possibly a clinical form of SD.