Americans have embraced a large number of diets in an attempt to manage obesity, improve quality of life, and address specific health problems. Among diets developed to address health problems, the ketogenic diet has had a long and variable history. Developed in the 1920s by a faith healer to help children with epilepsy, this diet induces a state that mimics carbohydrate starvation. As medications became available and effectively addressed seizures, the diet fell out of favor. During the last few decades, researchers and clinicians have learned that it can be useful in children and adults with refractory epilepsy and a variety of other conditions. Once again, pharmacists may encounter patients who are employing dietary management of serious health problems. This very high-fat diet almost eliminates carbohydrates from the patient's food selection. The result is the substitution of ketone bodies as a source of energy. Today's ketogenic diet has been modified with scientifically proven adjustments to increase palatability and help with adherence. Effective for some forms of epilepsy, the ketogenic diet also seems to have some utility in Alzheimer's disease, Parkinson's disease, and glaucoma, and many Americans are using it to lose weight. Consultant pharmacists may field questions about this diet, its potential to correct or alleviate health conditions, and its limitations. The article discusses the ketogenic diet's strengths, limitations, potential mechanisms, and use in a number of conditions with an emphasis on the elderly.