An electro-nystagmographic study of labyrinthine function was performed in 56 patients with adolescent idiopathic scoliosis (AIS)aged from 10 to 16 years. Forty-seven patients had major structural single curvatures, and nine patients had double-primary scoliosis and were analysed separately. Treatment was required in 36 cases while 20 were being observed only. Thirty healthy children of the same ages constituted a control group. Spontaneous nystagmus (SN) and positional nystagmus (PN) were found in 24 out of the 47 patients with single curvatures and in only one subject in the control group (P less than 0.001). No significant correlation was noted between direction of convexity and nystagmus. Neither did the frequency of SN or PN differ significantly between patients requiring treatment and patients submitted to observation only. Significant differences were observed in the caloric response between right and left scoliotic patients (P less than 0.05). The right convex patients had a sensitivity dominance in the right labyrinth and the left convex patients in the left labyrinth. There were no significant differences between right- and left-beating nystagmus. A dysrhythmic nystagmus occurred in the scoliotic patients with significantly increased frequency (P less than 0.05). The results are discussed with special reference to aetiology in AIS. It was difficult, however, to draw any definite conclusion as to whether the findings may indicate a causative factor in relation to the idiopathic curvature or whether they might be a feed-back effect from the deformed spine.