Hemolytic-uremic syndrome (HUS) is characterized by the clinical and laboratory manifestations of acute renal failure, thrombocytopenia and microangiopathic hemolytic anemia. In children, the majority of cases occur after an infectious diarrhea mainly associated with the serotype Escherichia coli O157:H7. We present a case of a 5-year-old boy with post-diarrhea HUS due to cryptosporidium. The child remained on peritoneal dialysis for 24 days. However, he had a full recovery of his renal function and 6 months later, his overall condition was still very good. This is a particularly interesting case, not only due to the exceptionally rare cause of HUS, that is, the cryptosporidium, but also because of the serious gastroenteritis caused by the cryptosporidium in an immunocompetent child. It seems that in cases of post-diarrhea HUS, apart from E. coli O157:H7, even the rarest causes of gastroenteritis should be investigated.