Routine measurement of spatial resolution of a gamma camera is normally performed through the use of a four-quadrant bar phantom or one of several commercially available resolution phantoms. These phantoms all provide a qualitative index of system resolution with the inherent assumption that any change in intrinsic resolution would be apparent in the bar/hole pattern image. However on nine gamma cameras, comparison of intrinsic resolution determined from the line spread function by NEMA standards and from visual estimation of a four-quadrant bar phantom image showed poor correlation. The purpose of this study was to design and evaluate a new test pattern which would provide a more accurate estimate of resolution. We developed a line resolution phantom (LRP) which consisted of a 16-cm-diameter lead disk with a series of horizontal and vertical slits. This phantom permits a quantitative estimate of intrinsic resolution (to within 0.5 mm) from a visual examination of the LRP image. Evaluation on nine gamma cameras showed good agreement between results obtained with the LRP and measurement of resolution from the line spread function. The LRP is a simple and inexpensive test phantom which should find applications in quality control and acceptance testing.