Self-expanding metal stents are claimed to prolong biliary-stent patency, although no formal comparative trial between plastic and expandable stents has been done. In a prospective randomised trial, we assigned 105 patients with irresectable distal bile-duct malignancy to receive either a metal stent (49) or a straight polyethylene stent (56). Median patency of the first stent was significantly prolonged in patients with a metal stent compared with those with a polyethylene stent (273 vs 126 days; p = 0.006). The major cause of stent dysfunction was tumour ingrowth in the metal-stent group and sludge deposition in the polyethylene-stent group. Treatment after any occlusion included placement of a polyethylene stent. In the metal-stent group none of 14 second stents occluded, whereas 11 of 23 (48%) second stents clogged in the polyethylene-stent group (p = 0.002). Overall median survival was 149 days and did not differ significantly between treatment groups. Incremental cost-effectiveness analysis showed that initial placement of a metal stent results in a 28% decrease of endoscopic procedures. Self-expanding metal stents have a longer patency than polyethylene stents and offer adequate palliation in patients with irresectable malignant distal bile-duct obstruction.