Giardiasis is usually asymptomatic. However, with heavy infection the child develops loose, foul-smelling, watery stools. Abdominal cramps and vomiting are common. Usually the infection resolves in a few days but it may become chronic. Chronic giardiasis may cause chronic diarrhoea with malabsorption leading to failure to thrive and malnutrition.

It is difficult to confirm the diagnosis by finding cysts in the stool. Therefore, diagnosis is usually suspected from the clinical history and confirmed when the symptoms and signs disappear after treatment.