Klebsiella is becoming a more commonly isolated mastitis-causing organism on dairy farms across the Northeast. We have traditionally thought of the most common gram-negative organism isolated on dairies as E. coli, but over the last 20 years, that has changed on some farms. While there is always a range on each farm of how the mastitis presents, we hear from farms about two basic clinical presentations with Klebsiella. One is a very severe clinical mastitis with cows becoming systemically ill and with very poor recovery rates. The second is a less severe clinical mastitis but a number of these cows become chronically infected with an elevated somatic cell count (SCC).