The objective of this work was to evaluate the clinical and serological profiles of patients with undifferentiated connective tissue diseases (UCTD) who had been followed for at least 1 year. The retrospective analysis (197495) was based on UCTD patients diagnosed on the basis of clinical manifestations suggestive of a connective tissue disease, and the presence of at least one non-organ-specific autoantibody. A total of 91 patients were evaluated. The condition of 79 remained stable during the follow up, while in 12 the UCTD evolved to systemic lupus erythematosus (SLE) within a mean period of 3 years (min. 1 year, max. 8 years, median 2 years) after the onset of the disease. At baseline none of the variables, considered alone, showed an association with the future development of SLE. Multiple regression analysis, however, suggested that the association of sicca symptoms, Raynaud's phenomenon and/or photosensitivity was inversely correlated with the development of SLE (P = 0.0012, Fisher's exact test). The most common clinical manifestations of UCTD included arthritis, arthralgias, Raynaud's phenomenon, xerostomia, xerophthalmia and leukopenia. The stable UCTD patients showed a simple autoantibody profile characterized by a single autoantibody specificity in 82% of the cases 30% with anti-Ro/SSA alone and 28% with anti-RNP alone. This profile remained stable during the follow up. Anti-RNP antibodies alone correlated with the presence of Raynaud's phenomenon and arthritis (P < 0.001 and P < 0.01, respectively), while anti-Ro/SSA antibodies alone correlated with xerostomia and xerophthalmia (P < 0.01). In conclusion, the UCTDs in most of our patients seem to represent distinct clinical entities with a limited autoimmune repertoire rather than the early phases of definite connective tissue diseases. They could therefore provide an ideal model for the study of the clinico-serological correlations in autoimmune diseases.