A utility vehicle (10) comprising a ventilation system (30) which receives air from the environment, filters the air and supplies the filtered air into a cab (18). The system comprises a fan (54) to drive air through a channel from the environment to the cab, and a main air filter arranged within a roof section (24) of the cab and downstream of a pre-filter. The pre-filter (32;72) rotates about a rotation axis which is substantially parallel to the air flow through the pre-filter so as to reduce the particulate matter which reaches the main filter. The rotation of the pre-filter (32;72) creates a centrifugal force which forces the particulate matter radially outwardly to reduce the build-up of matter on the filter, thus reducing the frequency of servicing. The pre-filter can be integrated into a cab ventilation system or provided in a module which can be added to a vehicle having a conventional ventilation system.