More than a thousand RA patients have been treated with cyclosporin A (CyA) in clinical trials. In seventeen of them, tumours developed after treatment with the drug. An indirect approach used to calculate the relative risk associated with the use of CyA in clinical trials suggested that: (i) RA itself increases the risk of cancer development; (ii) the use of CyA further increases the risk by approximately the same degree as DMARDs; and (iii) neither the pattern of malignancies nor the risk associated with CyA seems to be different from that observed with conventional DMARDs. Nevertheless, patients treated with CyA should be carefully monitored while more experience is gathered.