This study was carried out to determine the relationship between aflatoxins taken with feed, laminitis, lameness and impaired fertility. Lesions were identified in the claw and hock region, causing lameness in 45 cattle in an establishment of 300 Holstein dairy cattle. Of these lame cattle, 27 had cystic ovaries and 10 had cystic ovaries together with clinical metritis. The increase in lameness and fertility problems occurring in this herd, living under the same management and feeding conditions, was determined to start with the change in feed concentrates and, in order to investigate the relationship with mycotoxins, Aflatoxin B-1 (AFB(1)) analysis was carried out in the feed and Aflatoxin M-1 (AFM(1)) analysis was carried out in the milk of cattle both with and without illness. While a value above normal was determined in AFB(1) in feed concentrate, hay and clover, when compared to the milk of normal cattle, high values of AFM(1) were determined in the milk of lame cattle with cystic ovaries. It was concluded that alflatoxins taken with feed cause lameness (subclinical laminitis) and impaired fertility (cystic ovaries).