Connective tissue diseases (CTDs) are chronic multisystemic inflammatory disorders whose indicative signs or symptoms have a high sensitivity but poor specificity in predicting the evolution into a given CTD. We have analysed 84 consecutive patients initially diagnosed as having an early undifferentiated CTD (early UCTD) with the aim of verifying the evolution into one definite CTD and of evaluating the predictive value of clinical and laboratory parameters. During a 5-year study period, 33 patients developed signs of a full-blown CTD; the highest probability of evolution was in the first 48 months after the onset. Multivariate analysis allowed us to select those variables correlating with evolution into a particular CTD, such as sclerodactyly and oesophageal dysfunction for systemic sclerosis, xerostomia and anti-nuclear antibodies (SS-A pattern) for Sjögren's syndrome, and fever and anti-DNA antibodies for systemic lupus erythematosus. Furthermore, we assessed the prevalence of various clinical and laboratory manifestations, complications and prognosis of those patients diagnosed after a 5-year disease duration period as having a UCTD. In our series, major organs such as the kidney or heart seem to be spared, whereas we detected a relatively high prevalence of endocrine disease of autoimmune origin.