Abstract: Method in monitoring the condition of machines, in which method measurements are performed on a number of machines or machine parts to obtain quantities descriptive of the condition of the machines. In the method, characteristics or symptoms related to the operation or condition of the machine are derived from the measured quantities, a characteristic vector describing the current operational state of the machine is generated from the characteristics, characteristic vector categories are formed from characteristic vectors describing the same operational state, and a database is created in which are stored characteristic vector categories describing different operational states of the machines.