The aim of the study was to evaluate the relationship between the body condition of cows and their daily milk yield and composition of the milk. Body condition was assessed once a month (according to the 5-point BCS system) in a herd of 52 Black-and-White Polish Holstein-Friesian cows with annual milk yield of over 10,000 kg. The analysis covered 607 body condition assessments and test-day milking results. The data were analysed using the SAS package. Daily milk yield decreased significantly as BCS scores increased. Cows with the lowest BCS (≤ 2.25) produced 35.3 kg of milk, when for the highest scores (BCS > 3.75 pts) the amount of milk obtained amounted to 25.1 kg. Increasing body condition scores were accompanied by a significant increase in the content of protein, lactose and dry matter in the milk. Somatic cell count was not affected by body condition scores. At the beginning of lactation, multiparous cows used their energy reserves more intensively than primiparous cows, and from the sixth month replenished them to a greater degree. Lactations in primiparous cows were more persistent.