Congenital absence of shoulder girdle muscles is described in three generations of a family. The proband, a 3 year old boy, had absence of the sternocostal head of the right pectoralis major. His father had absence of the left serratus anterior and part of the left latissimus dorsi and his paternal grandfather had absence of the lower two-thirds of the left pectoralis major, with absence of the left serratus anterior and latissimus dorsi muscles. The condition is probably the result of a dominant gene. These observations show that absence of the pectoralis major is part of a wider spectrum of shoulder girdle defects. Where genetic advice is sought by persons with apparently sporadic absence of the pectoralis major, examination of the relatives is necessary.