Large, wide beams and thick slabs are frequently used as transfer elements where the total structural depth must be kept to a minimum. While these members provide large cross-sectional areas of concrete to resist shear demands, shear reinforcement may still be required. For these wide members, design codes do not provide guidance on appropriate limits for spacing of the shear reinforcement legs across the member width. This paper presents the results of 13 new experiments designed to investigate the influence of this spacing on the one-way shear capacity of wide reinforced concrete members. The capacity of members with well-distributed shear reinforcement could be safely predicted by the ACI 318 shear model, but stirrup efficiency decreased significantly as the stirrup leg spacing across the width increased. Limits are proposed on the spacing of stirrup legs across the member width to ensure that the shear reinforcement is effective.