The Large Bowel Cancer Project is a collaborative prospective study of 4228 patients with a histologically proven adenocarcinoma, of whom 2336 (55 per cent) survived a 'curative' resection. Follow-up information is available on 2220 patients (95 per cent). Subsequently, 309 (14 per cent) have developed a local recurrence confirmed by: biopsy (127; 41 per cent), clinical examination (77; 25 per cent), X-ray (15; 5 per cent), a raised CEA (2; 1 per cent), or some other method - e.g. CT scan or a confident unbiopsied laparotomy finding (88; 29 per cent). Statistically significant factors (chi2 test, P less than 0.05) associated with local recurrence are: Dukes' classification: A 4 per cent; B 13 per cent; C 18 per cent Tumour differentiation: Well 11 per cent; Moderate 14 per cent; Poor 21 per cent Obstruction: Absent 13 per cent; Present 21 per cent Perforation: Absent 13 per cent; Present 28 per cent Tumour mobility: Freely mobile 11 per cent; Others 21 per cent Operation performed (rectal and rectosigmoid tumours): Abdomino-perineal 12 per cent; Anterior resection 18 per cent; Surgeon (Consultant only): Range less than 5 per cent to greater than 20 per cent. Stratification of the above variables altered only the statistical significance pertaining to tumour differentiation (P less than 0.1, d.f. = 2). In particular, the differences between Consultant surgeons remained.