The aim of the present research was to compare the water requirements of grapevine in the regions of Bydgoszcz and Wrocław in the forty-year period between 1976 and 2015. In the research the authors used the mean monthly temperature values (°C) and monthly precipitation (mm) for the May-September period in the years 1976-2015. The meteorological data for the Bydgoszcz region was derived from standard meteorological measurements performed at the Experiment Station at Mochełek, and analysed at the Department of Land Reclamation and Agrometeorology of the UTP University of Science and Technology in Bydgoszcz. The meteorological data for the Wrocław region were provided by the Swojec experiment station of the Wrocław University of Environmental and Life Sciences. The grapevine water requirements were determined as optimal precipitation assumed by Kemmer and Schulz. It has been found that the grapevine water requirements in 1976-2015, expressed as the optimal annual precipitation according to Kemmer and Schulz, were higher in the Wrocław region than in the Bydgoszcz region and they amounted to 469.3 mm and 435.8 mm, respectively. The grapevine water requirements in both regions in the forty-year period under study showed a growing tendency. A larger increase in grapevine water requirements (27.5-28.0 mm per decade) occurred in the Wrocław region. The estimates show that during the forty-year period (1976-2015) the precipitation deficits in grapevine growing in the May-September period occurred in 11 years in the Bydgoszcz region and in 9 years in the Wrocław region.