The axial development of a paired co-rotating vortex system is experimentally studied in a square duct. The duct confines the vortex system. The co-rotating vortices are shed from a pair of NACA 0012 airfoils in a split-wing configuration. Lateral velocity fields are measured using particle image velocimetry. Time-averaged lateral velocity and axial vorticity fields are used to document the location of the vortices in the lateral flow field. The present study examines the effect of Reynolds number, lateral spacing, and angle attack on the development of the vortex system in a confined geometry.