Dysnatremias are a common clinical entity that are often associated with poor outcomes. This review takes a case study approach to understand how dysnatremias can result in devastating neurologic consequences. Concrete guidelines are provided for prevention, early recognition and treatment along with a discussion of how urinary electrolytes and osmolality can be used to guide therapy. Case studies in hyponatremic encephalopathy include the post-operative state, thiazide diuretics, extreme exercise and DDAVP use. Reasons to avoid using hypotonic parenteral fluids, risk factors for hyponatremic encephalopathy such as age, gender, and hypoxia, and the appropriate use of 3% sodium chloride are discussed. Case studies in hypernatremia include hypernatremia in the ICU setting and the emerging condition of breastfeeding-associated hypernatremia in infants.