The sonographic appearance of the sternocleidomastoid muscles of 36 children with congenital muscular torticollis was studied. Sternocleidomastoid tumour was detected in all of them and the images were more complex than described in the literature. A patchy echo-texture was as frequent as a homogeneous echo-texture, and was more common in the younger child. The echo-genicity of the mass could be hyperechoic, isoechoic or hypoechoic relative to normal muscle. A hypoechoic rim surrounding the mass was frequently present. Change of the proportion of the mass relative to the entire muscle-mass complex in different ages matching clinical observations was also noted. These sonographic findings would be important in establishing a sonographic diagnosis. The higher sensitivity of ultrasound in detection of sternocleidomastoid tumour over clinical methods, and the importance of the sonographic findings in the management of congenital muscular torticollis were also discussed.