A case of a 5-month-old infant with complete duplication of the right leg and ipsilateral renal agenesis is presented. There was also a duplicated scrotum, posterior urethral valves with hydronephrosis, abnormal pelvic bones, and a ventricular septal defect. Complete caudal duplication is exceedingly rare. Associated defects are common. Several aetiological theories have been proposed. Among them, an underlying polytopic (acro-renal) developmental field defect has been suggested. It best explains the specific findings in our patient. However, the aetiology of caudal duplication syndromes may be multifactorial. In the light of twinning theories, associated duplication of hindgut derivates should be suspected in similar cases. Further research is needed. The motor-skeletal functional outcome after leg duplication surgery is mostly favourable.
Conclusion: A case of complete unilateral leg duplication with ipsilateral renal agenesis is presented. It appears to support the theory of a polytopic developmental field defect.