The prevalence of mandibular dysfunction in a sample of 369 Israeli schoolchildren was found to be 56.4%, indicating that one or more of the cardinal symptoms were present. It increased with age from about 51% in the 10-13 year old group to 67.8% in the 16-18 year olds. The most common cardinal sign of dysfunction was joint sounds (35.8%), which increased with age from 28% in the youngest group to 44.3% in the oldest group. The second most common sign was joint sensitivity to palpation (30.4%), which showed a slight increase in the oldest group. Sensitivity of the superficial muscles was recorded third, with 20%. Joint pain and restriction of mandibular movement appeared infrequently. Two of the more common cardinal symptoms, namely joint sounds and muscle sensitivity, were statistically related to several possible aetiological factors and to age and sex. Analysis of association showed that the probability of muscle sensitivity increased in the presence of malocclusion and/or joint sensitivity to palpation. It also showed that age, occlusal wear, locking of the jaw and joint sensitivity to palpation increased the probability of joint sounds.