Startle modulation was induced by prestimulation in 43, 6–11 year old boys with attention‐deficit hyperactivity disorder (ADHD), 13 of whom were or had been enuretic, 17 age‐matched enuretic boys, and 42 age‐matched normal boys, using 60‐ms and 120‐ms prestimulation intervals and a 4000‐ms continuous tone. There was a significant multivariate effect of enuresis on startle amplitude modulation. This effect was attributed primarily to the reduction of amplitude inhibition following the 120‐ms prestimulation interval regardless of whether or not enuresis was associated with ADHD. There was no effect of ADHD on startle modulation by prestimulation. The inhibition following the 120‐ms prestimulation interval in the enuretic boys was reduced to the level of 5‐year‐old normal children, suggesting a maturational component of the deficient startle inhibition. The neurophysiologic dysfunction underlying the deficient startle inhibition in enuresis, but not ADHD, is discussed in terms of a possible dysfunction of mesopontine reticular mechanisms mediating preattentive processing of signals associated with spinal reflexes involved in urinary bladder control.