The prevalence of tic disorders and comorbid psychopathologies was determined in a community-based study of 1596 school children (age 9 to 17 years) conducted at the University of Rochester School of Medicine and Dentistry, NY. Using a standard psychiatric interview and standardized rating scales to diagnose behavioral disorders, 339 patients with tics were identified. Psychopathologies occurring more commonly (p<0.05) in children with tics included OCD, ADHD, separation anxiety, overanxious disorder, simple phobia, social phobia, agoraphobia, mania, major depression, and ODD. ADHD occurred in 38.4% of children with tics and 19.5% without tics (p<0.0001). Prevalence of OCD was 10.9% with, and 7.4% without tics (p=0.04); ODD 17.4% with, and 9.7% without tics (p<0.0001). By comparing the prevalence of neuropsychiatric disorders between children with and without tics, it was determined that these associations were not due to ascertainment bias or reactive asssociation but more likely, a shared neurobiologic mechanism, sometimes genetically determined. 
COMMENT. The common association of tic disorders, including Tourette syndrome, and ADHD and OCD is most probably due to a shared neurobiologic mechanism.
Fluctuations in frequency and intensity of tic and associated behavioral disorders were determined in 553 children (kindergarten through 6th grade) observed monthly from November 1999 to June 2000 at the National Institute of Mental Health, Bethesda, MD. . Monthly point prevalence of motor tics ranged from 3.2% to 9.6% (overall frequency 24.4%). Monthly point prevalence of behavioral problems ranged from 2.6% to 11.0% (overall frequency 25.7%). Incidence of motor tics and problem behaviors was 3 times higher during winter months. Tics in most children were transient, and observed on only one occasion. These usually involved eye blinks and facial tics. Behavioral comorbidity was associated with more persistent and involved tic symptoms.