Abstract: An insertion flowmeter apparatus for measurement of the fluid flow in a pipeline, particularly an oil and gas pipeline, utilizes a fluid-pressure actuated piston within a cylinder to insert and retract a stem having a turbine meter at the end laterally through the side wall of the pipeline. The retractable insertion flowmeter apparatus disclosed includes an hydraulic cylinder having a mounting flange on a first end for attachment to a flanged riser extending out of the wall of the pipeline, with an end plate provided on the second end of the cylinder. Both the mounting flange and the end plate have ports that communicate with the interior of the cylinder. A piston is disposed in the hydraulic cylinder for longitudinal movement therein in response to the introduction through the ports of pressurized fluid. The stem that carries the turbine meter extends longitudinally through the hydraulic cylinder and is secured to the piston.