Fasting during the month of Ramadan is one of the five pillars of Islam. During this month, adult Muslims are obligated to refrain from eating and drinking from dawn to dusk. Some of our CKF patients fast the whole month against medical advice, for many raisons (religious or social customs). The aim of our study is to evaluate the impact of fasting on the renal function in this population. We conducted retrospective study of 47 patients (16 females, mean age 61.9 years; 15-85 years) with a eGFR less than 90 ml/min/1.73m2, most had a eGFR less than 60 ml/min/1.73m2. For patients with chronic kidney disease, the existing data in the literature are scarce and give inconclusive results. Patients should be monitored closely by their physicians while fasting. If a sign or symptom of acute tubular necrosis occurred, the fasting should be discontinued