Numerous factors are believed to contribute to stuttering, although it is not completely understood what causes this disorder. Genetics play a role, as 60 percent of people who stutter have a family member who also stutters, according to the Stuttering Foundation. Some degree of temporary stuttering is normal during child development. This developmental stuttering occurs as children attempt to master more complex rules of grammar. It generally goes away once the child begins attending school. Developmental delays and other speech and language problems do contribute to more problematic, chronic stuttering, as well.

It also appears that people with long-term stuttering problems process language in an area of the brain that differs from the normal language-processing area of nonstutterers. Finally, people who stutter have difficulty connecting messages from the brain to the muscles and body parts that are used for speaking. Certain brain injuries (e.g., head trauma, stroke) can also cause stuttering problems in people who previously did not stutter.

Stuttering tends to affect males more often than females, with boys up to four times more likely than girls to stutter during elementary-school years, according to the the Stuttering Foundation.

It was once believed that stuttering resulted primarily from emotional disorders. However, it is now known that this disorder is not generally caused by emotional or psychological problems.

Those who stutter are no more likely to be diagnosed with such conditions than others in the general population. When they do occur, certain emotional problems may be due to stuttering (e.g., avoiding situations where stuttering is likely). However, a small number of patients may develop stuttering problems as a result of a mental illness (e.g., social phobia) or following traumatic events.