Eyes
You must have at least 20/40 near and far vision in each eye (tested separately). If you require glasses or contacts to meet this requirement, you must wear these at all times while operating an aircraft. You must not be color-blind and you must not have any conditions that interfere with your sight or are likely to interfere with your sight in the future.
Ears, Nose, Throat and Balance
Your hearing must be good enough to hear a person speaking in a normal conversational tone six feet behind you. You must not have any ear, nose, throat or mouth problems that are likely to interfere with speech communication or cause vertigo.
Mental Health and Substance Abuse
You must not have any mental condition that gives you hallucinations or causes "grossly bizarre" behavior. You must have no history of substance dependence or must demonstrate that you have totally abstained from using the substance in question for the past two years. Substances include nearly any potentially addictive or mind-altering chemical (including alcohol) except for tobacco and caffeine.
Seizures and Heart Disease
You must not suffer from epilepsy or any other seizure disorder which could impair your ability to fly a plane safely. You will be disqualified for many serious heart diseases, including (but not limited to) angina pectoris, myocardial infarction or other "coronary heart disease that has required treatment." A permanently implanted cardiac pacemaker will also disqualify you, as will a replacement valve or transplanted heart.
Diabetes and General Condition
If you have diabetes that must be controlled using insulin or similar product, you will be disqualified. In general, to become a pilot you must not have any condition which could cause you to suddenly lose consciousness, become disoriented or otherwise lose your ability to safely fly a plane. These requirements are not exhaustive, and some conditions may not permanently disqualify you from flying if you are otherwise qualified (in some cases, the examining doctor may defer judgment on a condition to a higher authority).