Unknown etiology is the commonest etiology of CRF in urban group and this can be explained by: presence of risk factors.Hypertension: is a common cause of CRF but is the first risk factor in most cases. Schistosomal diseases: still constitutes a health burden in rural areas. D.M. is a common cause of CRF especially in urban and semiurban groups. Chronic pyelonephritis and obstructive uropathy, are more common in rural areas and may be due to a role for bilharziasis. Kidney biopsy, may resolve some of the undiagnosed cases and should be done early before ESRD. Anemia: is a common association in different groups.