An adjustable drop nipple has an upper pipe with an inlet end adapted for connection to a branch pipe, and an outlet end. A lower pipe is telescopically and sealingly engaged with the upper pipe and has an inlet and an outlet including a connection for a sprinkler head. Upper and lower supports are respectively fixed to the upper and lower pipes. A vertical support member is positioned generally parallel to the longitudinal axes of the upper and lower pipes and is secured to the upper and lower supports by upper and lower fasteners, respectively. The upper fastener permits the vertical support member to travel axially upwardly upon an application of a primarily upward axial force, but prevents the vertical support member from traveling axially downwardly upon the application of a primarily downward axial force.