Truncation of the tumour suppressor adenomatous polyposis coli (APC) constitutively activates the Wnt/β-catenin signalling pathway. This event constitutes the primary transforming event in sporadic colorectal cancer in humans. Moreover, humans or mice carrying germline truncating mutations in APC develop large numbers of intestinal adenomas. Here, we report that zebrafish that are heterozygous for a truncating APC mutation spontaneously develop intestinal, hepatic and pancreatic neoplasias that are highly proliferative, accumulate β-catenin and express Wnt target genes. Treatment with the chemical carcinogen 7,12-dimethylbenz [a]anthracene accelerates the induction of these lesions. These observations establish apc-mutant zebrafish as a bona fide model for the study of digestive tract cancer.