The investigations were carried out in 1996–2005 on the fields of Agricultural Experimental Station Department of SGGW Chylice in Mazowieckie voivodeship. The occurrence of diseases was assessed in 1996–2000 on winter wheat cv. Kobra, and in 2001–2005 on cv. Mikon. Weather conditions in ten-year experimental period were differentiated and had a distinct influence on plant infection by pathogens, as well as on the level of winter wheat yielding. In the first part of experimental period (1996–2000) the weather was characterized by higher temperatures compared to long-term average and higher amount of rainfall, with the exception of the year 2000 when the summer drought occurred. The highest for that period grain yield (54.70 dt/ha) was obtained in 1998. This was related to the lowest total infection of leaf surface area (22.76%) and a relatively low index of infection of stem base by Tapesia yallundae. In that year mass of 1 000 grain was also the highest. The lowest grain yield (40.80 dt/ha) was recorded in 2000 due to summer drought. In 1997 characterized by a high level of infection by T. yallundae (eyespot) obtained grain yield was also relatively low. In the second part of the experiment conducted on cv. Mikon (2001–2005) the lowest grain yield was recorded in 2001 (28.85 dt/ha) when per cent of leaf area infection of 2 upper leaves by Puccinia recondita (brown rust) was very high (44.79%), and the highest yield was obtained in 2003 (57.27 dt/ha). This was due to a moderate level of total leaf infection (30.21%) with fungal pathogens and favourable weather conditions for wheat development. In that year mass of 1 000 grain was also the highest. The occurrence of stem base infection by Fusarium spp. was maintained in the years 1996–2005 on differentiated level and it was lower in earlier years compared to the later period. The infection of ears by Leptosphaeria nodorum and Fusarium spp. was usually not high and its influence on the amount of grain yield not clearly evident. Chemical control of diseases influenced grain yield increase which was the highest in 2001 when winter wheat leaves were heavily infected by Puccinia recondita. The yield increase on fungicide treated plots was in that year 53.15%. It was evident that brown rust may pose a serious threat to winter wheat in the years of its high occurrence.