Abstract: Apparatus for inhibiting sway and for applying the brakes of a trailer includes a sway sensor connected to a frequency-discriminating circuit which senses lateral oscillatory motion of the trailer and which generates separate right and left acceleration signals in response to right and left acceleration, respectively, of the trailer. A circuit produces a sway-inhibiting signal in response to both of said right and left acceleration signals which successively occur in a time shorter than a predetermined period of time. A braking-signal circuit produces a brake control signal in response to the sway-inhibiting signal, this brake control signal being utilized for applying the trailer brakes momentarily to correct for a sway condition.