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The invasive grass medusahead dominates millions of acres of rangeland across the West. While the ecological impacts of medusahead on rangeland ecosystem function have been well-demonstrated the economic impact of this and similar invasive species has never been quantified, severely limiting cost:benefit assessment of different management decisions.� The objective of this study was to quantify the relationship between medusahead abundance and beef cattle gain. We experimentally manipulated medusahead abundance in 9, 5-acre pastures for two years (2013-2014) using fire, seeding, herbicide and grazing to reduce medusahead abundance in some pastures while increasing medusahead abundance in other pastures. In March 2016, and again in March 2017 we stocked pastures with 6 steers (approximately 650 lbs. starting weight) in each of the 9 pastures. Pastures were grazed from March to beginning of May and we adjusted stocking rate (removing or adding animals) to achieve equal utilization across pastures by the end of the growing season (target 800 lbs. per acre dry matter).� We quantified forage production and utilization monthly across 10 transects as well as forage composition as frequency in mid spring and total animal gain across the grazing period. �There was little evidence that medusahead abundance influenced average daily gain in this trial (P > 0.05) but across both years increasing medusahead abundance reduced carrying capacity.� On average a 10% increase in medusahead abundance decreased gains by 30 lbs per acre over the growing season. ��Modest per acre inputs or changes in management that can progressively lower medusahead abundance are likely to produce a measurable economic and ecological benefit.