Rectal polyp count exceeding 20 (HR 30.99, 95 per cent confidence interval 9.57 to 100.32; P < 0.001), APC mutation codon 1250-1450 (HR 3.91, 1.45 to 10.51; P = 0.007), colonic polyp count 500 or more (HR 2.18, 1.24 to 3.82; P = 0.006) and age less than 25 years at the time of surgery (HR 1.99, 1.17 to 3.37; P = 0.011) were independent predictors of progressive rectal disease.