Telomerase is a reverse transcriptase enzyme contributing to the maintenance of the telomeric structure by adding telomere repeat sequences to chromosomal ends, thus compensating for its shortening. Telomerase activity which is common in cancers and human germ line tissue, may also be increased, although to a lesser extent, in systemic autoimmune diseases. We aimed to evaluate telomerase activity in a group of Turkish patients with various connective tissue diseases. In this cross sectional study, 19 patients with systemic sclerosis (SSc), 15 with systemic lupus erythematosus (SLE), 10 with rheumatoid arthritis (RA) and 14 with primary Sjögren's syndrome (pSjS) were studied. As the control group, 29 healthy subjects were also included. Human telomerase-specific reverse transcriptase (hTERT) was measured in peripheral blood lymphocytes, using online real-time reverse-transcriptase polymerase chain reaction (PCR). We also investigated if hTERT values in each patient group were correlated with clinical parameters and disease activity. Highest hTERT values were observed in RA group (21.24 +/- 28.54), followed by SLE (13.38 +/- 26.05) and pSjS (11.73 +/- 10.59) groups. Only hTERT values in RA group was significantly higher than the healthy control group (7.62 +/- 4.21) (p < 0.05). Interestingly, hTERT values in SSc were very low (2.09 +/- 3.18), even less than the healthy control group. In consistent with previous studies, telomerase activity was increased in SLE and RA. Very low telomerase activity in SSc group was rather surprising. Since existing telomerase data in SSc was limited and telomere shortening was previously reported in SSc, our finding of low telomerase activity in SSc group deserves relevant discussion and further studies.