To evaluate the prognostic criteria for identifying cows at an increased risk of a fatal outcome from acute Escherichia coli mastitis, the potential cut-off values for five diagnostic parameters associated with a high mortality were determined by receiver operator characteristic curve analysis. These criteria were hematocrit value >32%, blood non-esterified fatty acid concentration >0.4 mEq/l, antithrombin activity <120%, platelet count <15 × 10⁴/ml and presence of dysstasia. Exceeding the cut-off values for at least three parameters on day 2 after onset predicted fatality (predictive value 87.5). When these prognostic criteria were applied to 34 clinical cases, cows that met three criteria were seven times more likely to die than cows that met fewer than three criteria.