The aim of this study was to evaluate the occurrence of mastitis and its impact on the reproductive parameters in a herd of 180 dairy cows. Based on the herd records 127 cows of Slovak spotted cattle and their crosses with red Holstein were selected for study between 1—2 months after calving. The examination of the health status of the mammary glands consisted of: the clinical examination of the udder, the California mastitis test (CMT) supplemented by the collection of mixed milk samples, and the laboratory examination of bacterial pathogens causing the mastitis. In addition to the mammary investigation, reproduction indicators such as the length of the insemination interval, the service period, the intercalving period and the insemination index were also analyzed. The results of this study indicated: a high incidence of mastitis (41.6 %), especially latent (21.2 %), subclinical (15.7 %) and clinical (4.7 %) forms were most common in the herd. The most frequently isolated bacteria from the infected milk samples were: coagulase negative staphylococci (54.1 %),