A medical instrument for irrigation and/or suction has an instrument body in which at least one flow channel is present for the passage of a fluid, at least one shut-off member for alternately shutting off the at least one flow channel, and an actuating member for actuating the shut-off member. The at least one shut-off member is a ball which, in a closure position, lies sealingly on a sealing edge of the flow channel so that it closes off the internal cross section of the flow channel, the ball being movable, between the closure position for closing the flow channel and a release position for freeing the flow channel, substantially in a direction transverse to the longitudinal direction of the flow channel, and the actuating member for moving the ball between the closure position and the release position being movable in a direction transverse to the flow channel.