Abstract : Abstract Colon cancer is one of the most common cancers around the world. It is classified as the third cancer that affects humans. Many studies show risk factors for cancer. This study was designed as a reference study (retrospective). This study was conducted in Dhi-Qar Governorate at Al-Hussein Hospital, peace be upon him, and included the collection of colon and rectal tissue samples immersed in paraffin wax for patients with colon cancer, during the period from October 2020 to April 2021 at the age of 20 years The aim of the study is to diagnose the presence of the cryptosporidium parasite in the tissues of colorectal cancer patients by using polymerase chain reaction (PCR). The results of the polymerase chain reaction showed infection in Cryptosporidium parasite 13.3% (13) positive samples out of 75 samples, and infection in Cryptosporidium parfum 9.2% (9) positive samples. The study also recorded a discrepancy between infection rate and gender. The infection rate of Cryptosporidium (8) samples 66.7% and Cryptosporidium parvum (5). The study also showed the most prevalent stages of cancer and the most common stages in which Cryptosporidium are present. The study recorded the second stage of colon cancer patients with the most diagnosed stages, as well as the presence of Cryptosporidium in it (4) 33.3%. But Cryptosporidium recorded the most infection in the first stage of colon cancer (4) 50%.