Mastitis is defined as an inflammatory reaction of udder tissue to bacterial, chemical, thermal or mechanical injury, which causes heavy financial losses and milk wastage throughout the world. Until now, studies have focused on the economic aspects from which perspective mastitis can generally be considered as the most serious disease in dairy cows; however, costs are not the only negative consequence resulting from the infection. The environmental impact is also significant; milk is discarded, which means lower efficiency and hence a greater environmental impact per produced liter of milk. Less milk is produced, which leads to an increased need for calf feed, and meat production is also affected. The main aim of this paper was to quantify the environmental impact of mastitis incidence. A standard scenario (representative of present-day reality in Galicia, Spain) and an improved scenario (in which mastitis incidence rate is reduced by diverse actions) have been defined and compared using Life Cycle Assessment (LCA) methodology. Among the impact categories studied, acidification, eutrophication and global warming were found to be the most significant environmental impacts. In all these categories, it was revealed that a decrease in mastitis incidence has a positive influence as the environmental impact is reduced. Even if the quantitative results cannot show a considerable decrease in the environmental burden, the impact cannot be regarded as negligible when the total consumption or total production of a region is considered. For example, the outcome of the proposed improvement measures for Spain's greenhouse gas emissions can be quantified as 0.06% of total emissions and 0.56% of emissions by the agricultural sector.