Most children with diarrhea have no dehydration. However, some can be associated with dehydration. Presence of dehydration can be associated with pre-renal dysfunction and dyselectrolytemias which can adversely affect the outcome. The outcome therefore, rests on early diagnosis and treatment of dehydration. Hence present study was planned for clinical assessment of renal function in paediatric cases of acute diarrheal disease with dehydration. The study was planned in Upgraded Department of Pediatrics, Patna medical College and Hospital, Patna, Bihar. The study was conducted from the Jan 2015 to Nov 2015. Out of the total 930 childrens admitted to Department 112 cases were diagnosed with the acute diarrhoea. These were evaluated and discussed as follows. The data generated from the present study concludes that Acute Watery Diarrhea is more common cause for morbidity and associated with more abnormalities in renal function tests and electrolyte levels than Invasive Diarrhea. Derangements in renal function tests and serum sodium levels are seen with increasing severity of dehydration. In presence of clinical signs of dehydration, blood urea, serum creatinine and electrolytes mainly serum sodium levels should be assessed.