Background: A randomized comparison of D1 (level 1 lymphadenectomy) and D3 (levels 1, 2 and 3 lymphadenectomy) dissection was performed to evaluate morbidity and effects on survival from gastric cancer. Methods: A total of 221 patients were studied after resection for gastric cancer, 110 after D1 surgery and 111 after D3 surgery. Results: The morbidity rate was higher after D3 than after D1 resection (17.1 (95 per cent confidence interval (c.i.) 10.1 to 24.1) versus 7.3 (95 per cent c.i. 2.4 to 12.2) per cent respectively; P = 0.012). The difference was largely related to abdominal abscess (8.1 per cent after D3 versus none after D1 resection; P = 0.003). The D3 group had an anastomotic leak rate of 4.5 per cent whereas there was no leakage in the D1 group (P = 0.060). All anastomotic leaks were minor and were managed non-operatively with nutritional support. Patients who had D3 resection had longer operating times, greater blood loss and postoperative drain outputs, and more patients needed blood transfusion. There was no death in either group. The hospital stay was longer after D3 than D1 surgery (mean(s.d.) 19.6(13.9) (range 10-98) versus 15.0(4.0) (range 10-30) days; P = 0.001). Conclusion: Extended lymphadenectomy for gastric cancer is associated with more complications than limited lymphadectomy but this does not lead to significant mortality.