The present paper describes the results of measurements of electric and magnetic stray fields around three types of commercially available diathermy units with four very typical electrodes in six routine therapeutic treatments. The aim of the survey was to investigate the exposure to the physiotherapist and the exposure to unprescribed tissues. Field strengths were measured at 15 points close to the patient's body. At a distance of 0.6 m from the diathermy units the power density was less than 10 W/m2. With respect to stray fields the results showed that the diathermy devices are very similar but there are great differences between the electrodes during specific treatments. The results assist in selecting proper electrodes for various therapeutic treatments, as they indicate which electrodes would have minimal stray fields.