Stuttering is typically a developmental disorder beginning in early childhood and continuing into adulthood in at least 20% of affected children. The mean onset of stuttering is 30 months. Although there is variability, early stuttering behaviours usually consist of word or syllable repetitions, while secondary behaviours such as tension, avoidance or escape behaviours are absent. Most young children are unaware of the interruptions in their speech. With young stutterers, disfluency may be episodic, and periods of stuttering are followed by periods of relatively decreased disfluency.