Cryptosporidium parvum is a protozoan causing cryptosporidiosis. Primary symptoms are acute, watery, and non-bloody diarrhoea. The study analyzes the prevalence of cryptosporidium infestation in the immune-compromised patient and compares the same among immune-competent subjects within the same age group having complaints of diarrhoea. The study also helps in forming a scoring system relating the numbers of oocysts of cryptosporidium observed per oil immersion field with the CD4 counts of the immune compromised  patients to quantify the severity of the decreased immunity.