For years, people have speculated about famous people in history, whether they had ADHD or other mental illnesses. For example, lists on the internet show people such as Albert Einstein, Leonardo da Vinci, Thomas Edison and Alfred Hitchcock exhibited symptoms of ADHD. The website, BabeRuthCentral.com, states, "It was only discovered more recently, that Babe actually suffered from ADHD, which contributed to Babe's wild, hyperactive nature-both in childhood and at times as an adult. It is also believed that Babe's ADHD was a factor in his excellent baseball skills." 
It is impossible to say definitively that Babe Ruth had ADHD. Posthumous, or retrospective diagnosis, is normally done by historians and the media. In some cases, they may be right but there are a number of problems with diagnosing someone with anything other than a physical illness which can be documented with medical records or a new autopsy.
Diagnosing those who are no longer alive and able to participate in a medical exam comes down to being educated guesses. The diagnosis of ADHD is sometimes considered controversial because there is no lab or medical test which shows the presence of ADHD. When a child or adult is diagnosed with ADHD, doctors look at:
- A direct conversation with or observation of behaviors of the person
- School records
- Questionnaires filled out by teachers, parents or other significant people in the patient's life
- A discussion of symptoms, where they occur and how they interfere with daily life
For adults first being diagnosed with ADHD, it is helpful to have copies of school records or questionnaires completed by parents on childhood behaviors.
When diagnosing someone who has passed away, especially those who died many years ago, documentation is limited to written information. This may be in the form of diaries and journals written by the person, or various narratives about behaviors seen in the person by others. By today's standards, in many of these cases the limited documentation would not be enough to diagnose an illness.
In Babe Ruth's case, there is not only written documentation but first-hand accounts. Babe Ruth's early years were filled with getting into trouble. According to "Being Babe Ruth's Daughter" (ESPN), "George Jr. (Babe) roamed the waterfront dodging truant officers, hurling stolen tomatoes through plat glass windows, chewing tobacco, dipping into his father's till (his father operated a saloon) and emptying glasses left behind by his patrons." 
In 1902, when Babe Ruth was 7 years old, he was declared "incorrigible or vicious" and was committed to St. Mary's Industrial School. It was at this school he met Brother Mathias, who coached the ball club and encouraged Babe to try out. For years, he coached Babe, spending hours playing catch and grooming him to be a pitcher.
The article on ESPN states, "Today's language for unmanageable boys is a diagnostic code: Attention Deficit Hyperactivity Disorder. Donna believes her grandfather had ADHD, which she saw in her late brother. A conversation with a family friend, Juanita Jennings, fueled her suspicions. 'She described the social life, showing up at 11 p.m. for dinner parties, the round-the-clock partying,' Donna said. 'He slept a couple of hours a night, and a couple of hours was good.' " 
While we will never know whether Babe Ruth, Albert Einstein, Leonardo da Vinci, Thomas Edison or Alfred Hitchcock actually had ADHD, it makes sense that there are people throughout history that had symptoms of ADHD. Today, statistics estimate that around eight percent of the population have ADHD and about five percent of the adult population still show signs of ADHD. Even though ADHD is a relatively new diagnosis, we know there are written reports of symptoms of ADHD as far back the 1800s. ADHD hasn't just arrived, it has been around, taking on different names and, at times, different symptoms have been emphasized. But it doesn't make any sense to think that throughout history there are not those who have been impacted by ADHD.
See also: Celebrities With ADHD
 "Babe's Personal Side," Date Unknown, Staff Writer, BabeRuthCentral.com
 "Being Babe Ruth's Daughter," 2011, Dec 18, Jane Leavy, ESPN.Go.com: Grantland