If you bring a Chao to the doctor, he will take a look at it for you. He can tell you the strengths and weaknesses of your Chao, and explain how it is feeling. There are two options available when you visit the Chao Doctor: "See the doctor", and "Medical chart".
See the Doctor
When you pick the "See the doctor" option, the Chao Doctor will examine your Chao carefully. He will tell you whether it is sick or healthy, and will advise you on how to look after it. If your Chao gets sick, take it to the doctor!
You can tell when your Chao gets sick because it will start coughing and groaning in the Chao Garden. If this happens, you should take it to the Health Center right away, and choose this option. The Chao Doctor will examine your Chao and give it medicine to help it feel better!
When you pick the "Medical chart" option, the Chao Doctor will let you read your Chao's medical records. These records include very detailed information about your Chao! Most of these details can only be seen here. There are three pages in the file: use the L and R buttons to switch between them.
The blue page shows the basic information about your Chao. You can see the name of your Chao at the top, and a picture of it on the right. The alignment and first evolution of your Chao are displayed on the left; the file refers to them as "Attributes" and "Ability type", respectively. The bottom of the blue page shows a table showing your Chao's main stats; Intelligence and Luck are still both hidden. However, you can view your Chao's stat grades here, and this is the only place you can do so. You should always check the stat grades of all of your Chao!
The yellow page shows some more advanced details about your Chao. First, your Chao's personality is displayed. This is followed by your Chao's favourite fruit; try to feed it this to make it happy! Next, the record shows your Chao's age and its number of transformations. Please note that "transformations" means reincarnations, not evolutions. Finally, this page shows the current condition of your Chao; that is, whether it is health or sick.
The pink page shows your Chao's competitive records from the Chao Stadium. You can see all of the medals that your Chao has won from the Chao Races, as well as its wins, losses, draws, and rank in Chao Karate.
Below are all the illnesses your Chao can get, and medicine that the Chao Doctor will give it to recover.