The rates of concurrent TS and OCD in the current study are consistent with those of two prior, school-based studies that identified OCD in 16%19 and 19%4 of children with TS. A third, smaller school-based study identified only seven children with TS, none of whom had OCD, placing their point estimate of co-occurring OCD at an upper limit of 14% (<1 in seven).17 Together, these data suggest that co-occurring OCD is less common in TS cases derived from population-based studies compared with those from clinically ascertained samples. Although one community-based study of 17-year-old Israeli army recruits identified OCD in 42% of TS subjects,15 this rate is not necessarily comparable to those in other studies, as OCD may be more prevalent in adolescent TS patients compared with school-age children.3,29
