We discuss the clinical and serologic features of 27 patients with overlap syndrome followed prospectively by our group. The findings are similar to those of other reports, but we have drawn attention to the presence of peritendinous nodules in these patients and mentioned some peculiar neurologic manifestations. Rheumatoid arthritis was the most common diagnosis in our patients. The presence of high-titer antibodies against the nuclear ribonucleoprotein fraction of extractable nuclear antigen (nRNP) did not allow the identification of a particular subgroup. However, patients with this antibody tended to fulfill more criteria of more diseases than those without it. The findings lead us to conclude that antibodies to nRNP do not identify a particular subgroup within the overlap syndromes and that mixed connective tissue disease does not appear to be a distinct entity.