Abstract: An automatic steering system and method are provided for a vehicle including an hydraulic primary steering system. The automatic steering system includes a guidance module with a GPS receiver and a microprocessor adapted to process and store GPS data defining travel paths, which can be associated with a cultivated field in an agricultural vehicle application. An automatic steering module is connected to the guidance module and to a steering valve control block, which provides pressurized hydraulic fluid in parallel with the vehicle's primary hydrostatic steering system. The automatic steering system utilizes a constant factor, such as steering rate, for predictability and simplicity in the operation of the automatic steering system. A feedback loop from the vehicle hydrostatic steering system uses the vehicle's actual turning rate for comparison with a desired turning rate.