An exhaust system for an agricultural and/or industrial tractor (10) having an internal combustion engine (11) located in an engine compartment covered by an engine hood (11a). The system includes an exhaust gas treatment unit (16) located inside the engine compartment hood and having a main chamber (18) fed by an inlet pipe (15) which receives exhaust gases from the engine and an outlet pipe (17) which passes treated gases into a final portion (14a,14b) of the exhaust system. The inlet and outlet pipes (15,17) are non-aligned and extending alongside the main chamber (18) in opposite directions to reduce the overall length of the treatment unit. The treatment unit (16) may be installed above the engine (11) with the exhaust gases passing through the unit either generally normal or parallel to the direction of driving (D) of the tractor.