Approximately 45 Holstein cows that were Mycobacterium paratuberculosis-positive on the basis of fecal culture were maintained at any one time in a 210-cow dairy herd. Farm management participated in the New York State Paratuberculosis Eradication Program. Paratuberculosis-positive cows were grouped separately from negative cows, but they were otherwise managed identically. During a 1-year study, 180 paratuberculosis-negative cows and 113 clinically normal paratuberculosis-positive cows were identified. From paratuberculosis-negative cows, 6, 100 quarter milk samples were aseptically collected for microbiologic culture of mastitis pathogens, and 3, 129 quarter samples were obtained from paratuberculosis-positive cows. Dairy Herd Improvement Association (DHIA) records were used to monitor milk somatic cell count linear scores (LS), mature equivalent (ME) milk production, new mastitis infections, and chronic mastitis infections. Overall, paratuberculosis was associated with economic benefit due to lower rates of mastitis in positive cows, but a net financial loss resulted because of reduced milk production and increased culling rates.