Abstract Six thousand nine hundred and nineteen temporomandibular joint sounds made by 110 patients in 2200 opening- and-closing cycles were classified and analysed. On average there were three TMJ sounds in each cycle. Fifty-nine per cent of the sounds occurred on opening and 41 per cent on closing. Only 27 per cent of the sounds were clicks and 73 per cent were crepitus. The average duration of hard TMJ clicks, excluding background crepitus, was 10 ms and the average duration of soft clicks was 14 ms. Eighty-six per cent of all the sounds (clicks and crepitus) were soft and 14 per cent were hard. Ninety-four of the patients were studied more closely: 17 had only opening clicks, 7 had only closing clicks and 43 had reciprocal sounds; 28 had groups of 20 consecutive sounds, but in only 5 did they occur in both opening and closing. The significance of these findings is discussed.