This study provides up-to-date findings on lactose malabsorption, lactose intolerance and genetic predisposition to adult-type hypolactasia in 72 patients after restorative proctocolectomy (RPC). The lactose malabsorption was assessed by hydrogen-methane breath test. Genetic predisposition to adult-type hypolactasia was assessed by detecting -13910T/C polymorphism in the lactase gene. Lactose intolerance was more frequent in UC (ulcerative colitis) patients than FAP (familial adenomatous polyposis) patients (77.5% vs. 55.2%; p=0.01). The C/C genotype of the lactase gene was observed in 39.1% subjects with no significant difference between UC and FAP patients. Lactose malabsorption occurred in 10.1% of subjects and almost only in patients with genetic predisposition, with the same frequency in UC and FAP patients.