BACKGROUND: Enteric infection by Giardia intestinalis is a common cause of diarrhoea world-wide and a significant cause of morbidity in children. AIM: To compare the efficacy and safety of nitazoxanide and metronidazole in the treatment of diarrhoea caused by G. intestinalis in children. METHODS: A total of 110 children presenting with diarrhoea caused by G. intestinalis were randomized to treatment with either a 3-day course of nitazoxanide (100 mg b.d., age range 2-3 years; 200 mg b.d., age range 4-11 years) or a 5-day course of metronidazole (125 mg b.d., age range 2-5 years; 250 mg b.d., age range 6-11 years). The patients were followed-up for a determination of clinical response 7 days after the initiation of treatment, and two subsequent stool samples were collected for parasitological examination. RESULTS: Diarrhoea had resolved in 47 children out of 55 (85%) in the nitazoxanide treatment group before the day 7 follow-up visit, compared to 44 out of 55 (80%) for metronidazole. Diarrhoea resolved within 4 days in most cases. Only mild, transient adverse events were reported. CONCLUSIONS: A 3-day course of nitazoxanide suspension is as efficacious as a standard 5-day course of metronidazole suspension in treating giardiasis in children.