Cystoisospora belli , formerly known as Isospora belli, protozoal parasite endemic to many regions of the world including the Caribbean, Central and South America, Africa, and South-East Asia. It is frequently encountered in patients with acquired immunodeficiency syndrome (AIDS) and is considered to be an AIDS-defining illness. Chronic severe watery diarrhoea due to C. belli has also been reported in other immunodeficiency states. C. belli infection in immunosuppressed patients has rarely been described. We describe severe diarrhoea due to C. belli in a human immunodeficiency virus-negative renal transplant recipient on immunosuppressive drugs. Oocysts of C. belli were detected in direct smear preparation of the diarrheic stool sample of the patient. The patient responded to combination treatment with Bactrim-double-strength (trimethoprim-sulfamethoxazole) and Nitazoxanide.