Cryptosporidum is a common intestinal protozoan in animals It has been recently found as an important cause of diarrhea in immunocompetent persons and as an apportunistic agent in patients with immunodeficiency, including AIDS cases. In September 1985 a survey was made in 400 soft and liquid stool samples obtained from clinical laboratories in Medellín, Colombia and 10 Cryptosporidium cases were indentified. The diagnosis was made by identification of oocysts in the stools concentrated, using the formalin-ether method and stained with modified Ziehl-Neelsen technic. Six cases were children younger than five years old and the rest were older than 30 years. There was no difference in sex distribution. All patients had diarrhea with an average duration of 13 days; 6 patients had also abdominal cramps and four patients had nausea, vomiting and fever. Only one, 53 years olds patient had leucopenia; the remainder were aparently immunologically competent. In two cases Entamoeba histolytica and in one case Giardia lamblia infections were associated.