The diagnosis of sleep-related bruxism is easily established clinically. When there is no identifiable underlying cause, it is classified as primary or idiopathic. However, secondary-symptomatic-forms are much more commonly observed and should therefore be questioned. In this case report, a 17 year-old boy was presented who admitted to our Sleep and Disorders Unit complaining of bruxism in his sleep but diagnosed as having secondary sleep related bruxism associated with arousals secondary to periodic leg movements in sleep. Especially in cases resistant to treatment, secondary conditions and possible underlying sleep disorders should be well-questioned and polysomnography should be performed even it is not necessary for the clinical diagnosis of sleep related bruxism.