Rash causing viral diseases may be transmitted during pregnancy, causing severe congenital disease. Although neurological and psychiatric disorders are common consequences of congenital rubella, children born to women who developed a viral rash during pregnancy do not appear to be at increased risk of these disorders if they were asymptomatic at birth. In a case-control study conducted to evaluate risk factors for ADHD, we found an increased risk of this disorder among children born to women experiencing a viral rash during pregnancy. The viral rash (i.e. measles, varicella, or rubella) was reported by 4 of 71 mothers of children with ADHD and none of the 118 controls' mothers (P<0.01). The difference remained statistically significant after adjusting for potential confounders (i.e. other factors found associated with ADHD, such as gender and familiarity). Although, the viral disease reported by the mothers, in accordance with their physician's diagnosis, did not represent a homogeneous nosological group, the unexpectedly high rate found among ADHD cases' mothers suggest a role for viral diseases occurring during pregnancy in the development of ADHD.