We describe the magnetic resonance (MR) findings in patients with gastrointestinal polyposis syndromes using breath-hold T1-weighted sequences, both standard and with fat suppression, prior to and following gadolinium administration, and breathing-independent single-shot half-Fourier RARE T2weighted sequences. Six patients with gastrointestinal polyposis syndromes underwent MR examination to investigate for the presence of metastatic disease. The appearances of the gastrointestinal polyps on noncontrast T1-weighted spoiled gradient-echo (SGE), T2-weighted (half-Fourier RARE) images, and early and late gadolinium-enhanced SGE images were determined. Other gastrointestinal findings and extragastrointestinal disease were also evaluated. Patients with the following gastrointestinal polyposis syndromes were included: familial polyposis (n โซุโฌ 3), Peutz-Jeghers syndrome (n โซุโฌ 1), Gardner's syndrome (n โซุโฌ 1), and neurofibromatosis (n โซุโฌ 1). Polypoid lesions in all patients exhibited signal intensity comparable to bowel on noncontrast images and enhanced similar to bowel on early and late gadoliniumenhanced images. Polyps larger than 2 cm, observed in one patient with familial polyposis and the patient with Gardner's disease, showed mild heterogeneity on late gadoliniumenhanced fat-suppressed images. Multiple colonic polyps ranging from 5 mm to 3 cm in diameter were observed in patients with familial adenomatous polyposis. A solitary 1.5 cm polyp associated with entero-enteric intussusception was observed in the patient with Peutz-Jeghers syndrome. Gastric polyps ranging from 5 mm to 6 cm were observed in the stomach of the patient with Gardner's syndrome. Duodenal and jejunal neurofibromas ranging from 1 to 2 cm in diameter were present in the patient with neurofibromatosis. Extra gastrointestinal findings included an adrenal adenoma (1 patient), a pheochromocytoma (1 patient), and liver metastases (2 patients). Gastrointestinal polyps in patients with polyposis syndromes may be visualized on MR images employing breathhold T1-weighted and breathing-independent snapshot T2weighted techniques. Appreciation of polyp enhancement on post-gadolinium images is an important finding, which should help distinguish polyps from bowel contents.