The benefits of drainage with respect to improving yield level and stability was recognized millennia ago, hence drainage is an old agronomical practice. However, agriculture is under constant change, and few long-term field studies exploring the need for drainage have been conducted in modern north European agricultural systems. The objective of this study is to describe yield variations in modern cereal crops as a function of the different dynamic drainage conditions that may appear in ordinary agricultural fields with old drainage systems, to this end seven years of field experiments were conducted at up to 3 field locations per year and with different N application levels. Drainage conditions were quantified annually in an index (SEW60) accumulating on a daily basis the depth of shallow groundwater (< 60 cm beneath the soil surface). Yield reductions up to 25 % was caused by poor drainage, despite that no visual plant symptoms were observed during the growing season. The yield variation across years, crops, and locations could be explained by SEW60. Yield effects of poor drainage were not significantly different for the investigated N-fertilization levels. This indicates that other factors than N are important for reduction of the yield potential induced by poor field drainage. The results clearly show the importance of good drainage as basis for agriculture in a region with excess precipitation, and they emphasize the need to focus on drainage conditions in a changing climate with increasing winter precipitation. Additionally, this can be a considerable factor in future water management trying to reconcile environmental and agricultural needs.