Diagnosis is the process of making big decisions with little information. The big decisions are made at the bedside through the patient’s history and physical findings. The little information which every student of medicine possesses is acquired from readings, discussions, lectures, and seminars. Why then is only a little information needed to make a diagnosis? Because, no matter how knowledgeable we are, our medical knowledge is merely a small drop compared to the ocean of medical literature. So, what is important or essential in order to practice sound and effective medicine? Is it the large excellent, exhaustive 3000 page textbook sitting on the shelf, which is only occasionally read? Or is it the 100 page bare bone essentials that barely scratches the surface of medicine?! This was my dilemma when I was a medical student and, later, a resident. All I needed was a small, informative book that provided me with rapid and thorough review of internal medicine without quantity of detail but with the vital information to serve as the foundation for the practice of medicine. While teaching medical students and residents over the past decade, I found out that this problem was, unfortunately, still alive and well. This manual is an attempt to provide what is needed to reach a quick and correct diagnosis of the most common symptoms seen in medical practice today.