Abstract: In a method for hydrodynamic focusing of a laminar and planar sample fluid flow, a system is provided for analysis and/or sorting of microscopic objects in the sample fluid comprising an optical objective for optical inspection of the microscopic objects. Microscopic objects are conveyed in the laminar flow of the sample fluid, and two laminar and planar flow of sheath fluids are provided. The flow of the sample fluid is hydrodynamically focused at an optical inspection zone of the system by the sheath fluids. Focusing of the flow of the sample fluid is controlled such that all of the microscopic objects in the sample fluid are caused to be conveyed in a common flow direction in one single plane at the inspection zone of the system, and the microscopic objects in the fluid are optically inspected through the optical objective.