Maintaining crop rows in drip irrigated fields at precisely the same horizontal distance to subsurface drip irrigation laterals, year after year, is very difficult. Crop row to drip lateral distance directly affects seed germination and plant development, particularly in areas of limited irrigation capacity. Many new SDI systems are being installed with GPS guided tractors to improve positional accuracy. A SDI system was installed in July 2005 at the TAES research facility at Halfway for an experiment documenting the affects of drip tape horizontal distance relative to planted cotton row. Drip tape was installed at a depth of 13 inches from level soil surface in a 4-acre area using a GPS guided tractor with RTK (Real-time Kenematic) accuracy. The software program ArcGIS9 was used to create shape files (polylines) that provided input for tractor guidance during installation. Following SDI installation, tape laterals were manually excavated at 192 sites in the field and their actual locations were referenced. This paper describes the relative accuracy of the final drip tape installation. Differences in desire to actual tape location followed a normal probability distribution with 55% of the tape laterals being with one inch of their desired location, 86% within two inches, and 99% within three inches.