Disrupted sensorimotor gating has been found in various neuropsychiatric conditions which are characterized by impaired attention, poor impulse control, dysfunctional dopamine neurotransmission, and neurodevelopmental deficits. We investigated sensorimotor gating by prepulse inhibition (PPI) of the acoustic startle eyeblink reflex in 23 young adults diagnosed with attention deficit hyperactivity disorder (ADHD) as children and still symptomatic at the time of testing and 29 age-matched healthy control subjects. Sensorimotor gating was assessed in a passive listening task at prepulse-to-startle probe intervals of 30, 60, 120, 240, and 480 ms, and subsequently at prepulse-to-startle probe intervals of 60, 120, 240, and 480 ms whilst participants were performing a two-tone auditory discrimination task on the prepulse. Consistent with increased neural maturity and partially remitted symptomatology, our results indicate intact sensorimotor gating for both tasks in adult ADHD with no comorbidity, independent of the subjects' gender and whether ADHD subjects were receiving ongoing stimulant treatment or not. Reduced PPI at 120-ms lead intervals, on the other hand, was recorded in a subset of 10 ADHD subjects who were taken off their prescribed regular stimulants for 24 h and tested in a randomized counterbalanced order for on vs. off medication. However, our data remained inconclusive as to whether this observation constitutes beneficial treatment or acute stimulant withdrawal effects on sensorimotor gating.