BACKGROUND: Patients with familial adenomatous polyposis (FAP) are colectomized in young age in order to avoid development of colorectal cancer. Because colectomy radically changes gastrointestinal physiology, and food avoidance may be present, colectomized patients may be at risk for nutritional deficiency. AIM OF THE STUDY: to evaluate: (1) serum biochemical levels as compared to reference; (2) dietary intake as compared to the recommendations. METHODS: Blood samples, interviews and food frequency questionnaire were collected from 38 colectomized FAP patients with duodenal adenomas (mean age 40 years, range: 24-70). They were recruited from the Norwegian database on FAP. RESULTS: Serum albumin was significantly higher (P < or = 0.0001), and Mg (P = 0.02), ferritin (P < or = 0.001), and cholesterol (P = 0.03) significantly lower, than reference levels. Compared to recommendations, a low intake was seen for folate and fiber (<50%), iron, thiamin, riboflavin (< 25%), and omega-3 fatty acids (8%). Sugar intake exceeded the recommendation, mainly due to a high intake of soft drinks. Food avoidance was reported by 53%. CONCLUSIONS: We would suggest that the nutrient intake among FAP patients should at least meet the recommendations for healthy subjects. Their risk of metachronous cancers should also cause special attention to dietary factors that may prevent nutritional deficiency and carcinogenesis.