A 56 year-old male patient had a gastric resection (Billroth II) at age 33. In 1993 he had vague upper digestive complaints. During investigations for a moderate anaemia biopsies performed during an oesogastroduodenoscopy revealed a jejunitis with Giardia lamblia (G.l.) trophozoites which were also found on the gastric mucosa associated with Helicobacter pylori related chronic active gastritis. The few publications dealing with the presence of Giardia lamblia in the stomach either assert or cast some doubts on the pathogenicity of this protozoa for the gastric mucosa. Gastric involvement by G.l. is usually associated with duodeno-jejunal disease responsible for diarrhoea which may occur as epidemics of varying extension. Since Giardia lamblia infection is not submitted to reporting in Switzerland, the epidemiology in our country is scarcely known and investigated. In our opinion, however, health authorities in Switzerland should consider the need of reporting this infectious disease.