Temporomandibular disorders (TMDs) were investigated in 143 pretreatment orthodontic patients (43 males and 102 females) whose age ranged between 10-25 years at the College of Dentistry, University of Baghdad, Iraq. The study was undertaken to elucidate the prevalence and severity of TMDs in malocclusion patients and to defme the relationships between malocclusion and TMDs. The clinical signs and subjective symptoms were recorded according to the principles introduced by Helkimo (1974b). Subjective symptoms were reported by 65.7% of the patients with 22.40/0 described as severe, and the most common symptoms were TMJ sounds and feeling offatigue. Clinical signs were observed in 81.8% of the sample with 22.4 and 6.3% described as moderate and severe, respectively, and the most common signs were muscle and TMJ tenderness to palpation. Significant sex differences were few and weak. However, tenderness to palpation decreased with age and dysfunction increased with age. Recurrent headache was reported by 38.5% ofthe sample, significantly more by females than males. Oral parafunctions were found in 78.3% ofthe patients, with females significantly more aware of orofacial parafunctions than males. Dental wear was observed in nearly all the patients increasing in severity significantly with age for all dental regions~ Class II malocclusion, both divisions 1 and 2, were unrelated to TMDs, while an overjet greater than 8 mm and an overbite of 5 mm or more predisposed to TMDs. True class III malocclusion and reversed overjet were associated with TMDs, while postural class III malocclusion, forward mandibular displacement and open bite were not. Inverted incisors and posterior crossbite were positively associated with TMDs signs, especially bilateral posterior crossbite. Upper anterior crowding appeared to predispose to TMDs, while lower anterior crowding, upper and lower anterior spacing were negatively associated with TMDs. The results of this study show that TMDs are more prevalent in orthodontic patients than in general population indicating the adverse effect of malocclusion on the function ofthe masticatory system; and that the incisor relationship is more important than the general occlusion (Angle's classification) in predisposing to TMDs.