Abstract: The involvement of Cryptosporidium in infantile diarrhoea was investigated among 200 children with diarrhoea who attended the Children Emergency Ward of the University of Calabar Teaching Hospital (UCTH) and Out-Patients Department of the General Hospital, Calabar, Nigeria. Another subset of 100 apparently healthy non-diarrhoeic children of comparable age range were used as controls. Stool samples collected from the test and control groups were examined for the presence of intestinal parasites including oocyst of Cryptosporidium using standard parasitological procedures. Cryptosporidium oocyst was found in 52 (26%) of the diarrhoeic stool samples and 8 (8%) of the non diarrhoeic control samples respectively (p<0.05). Cryptosporidium occurred as a single infection in only 32 (16%) of the 200 diarrhoeic subjects examined. The highest prevalence of cryptosporidiosis occurred among subjects aged 2/12-1 year. Infection was not detected in those aged ≥8 years. Other intestinal parasites detected were Ascaris lumbricoides (19%), Trichuris trichiura (2%), Hookworm (1%) and Entamoeba histolytica (1%). This study has demonstrated the involvement of Cryptosporidium as one of the aetiologic agents of infantile diarrhoea in Calabar, Nigeria. The study has made a case for the routine screening of stool samples of children with diarrhoea for the presence of Cryptosporidium before administrating prompt and appropriate therapy.