With the objective to know the mastitis cost for milk producer, was developed this study, with duration of a year in a milk farm of the North region of Sonora. The cost of the clinical and subclinical mastitis was estimated, taking into account the milk production, treatment costs and commercial milk value. The information was recorded monthly, the incidence of subclinical mastitis was obtained using California MastitisTest (CMT) and clinical mastitis incidence was obtained from farm health records. Was an incidence average of 18,3% of subclinical mastitis, whereas the incidence of the clinical form of mastitis was of 5,35%. The average monthly cost of each animal with mastitis was $185.40; altogether the mastitis had a cost of $30.966,34 annually, corresponding $12.470,75 (40,3%) to subclinical mastitis and $18.459,59 (59,7%) to clinical mastitis. Diseases total cost represents a third part of annually obtained milk production in the milk farm.