In Canadian and probably most US feedlots, Mycoplasma bovis pneumonia with or without concurrent arthritis is found in a high percentage of antibiotic nonresponsive, chronically sick cattle. Extensive multifocal yellow areas of caseation-like necrosis with sequestra formation are characteristic lesions. Subacute to chronic fibrinous or fibrosing pleuritis may accompany the lung lesions. Arthritis with similar necrotizing lesions of adjacent soft tissues, including tendon sheaths, are present in some cases. Characteristic gross lesions, unique histologic lesions and confirmation by IHC demonstration of M. bovis in these lesions are the best diagnostic tools in our experience. This chronic pneumonia and polyarthritis syndrome (CPPS) is a very costly syndrome in the feedlot industry, and management changes will probably be needed to control the problem. Vaccines are unlikely to be the solution to this problem. Prevention of transient BVDV infections is a scheme that may be beneficial, but more experimental work is required to confirm this.