Background: In embryology uterus, upper 2/3 of vagina and fallopian tubes derived from paired mullerian ducts. Crosby proposed fusion of the two Mullerian ducts starts caudaly in Muller's tubercle, proceeds cranially up to the fundus. Failure of ducts to develop leads to types of uterine, cervical or vaginal agenesis while incomplete fusion results in uterus didelphys. These congenital anomalies occur in 1-15% of women associated with renal anomalies especially agenesis or ectopia. This association can be attributed to additional disturbances in other mesodermal structures. Objectives: A 32 year c/o primary amenorrhea, intermittent left iliac fossa pain and failed to develop external sexual characteristics. As a child she had hypercalcaemia, asthma, renal scaring and myopia. Had bilateral femur deformity surgery, Sting procedure, strabismus repair and septoplasty. O/E BMI 15.1, Tanner 1 breast development and pubic and axillary hair present. MRI showed evidence of unicornuate uterus in the left iliac fossa. Also right lower pelvis close to the ovary was evidence of atrophic unicornuate uterus, no identifiable vaginal vault, free fluid within the pelvis and the ovaries looked normal. Chromosomal analysis showed 46XX. Bloods revealed normal IGF, FSH, LH and low Oestrogen levels. Results: One case been reported with unicornuate uterus with two cavitated non-communicating rudimentary uterine horns (Nez., Sm.) but, the horns are on top of each other. In our case a non-caviated, non-communicating rudimentary horns laterally placed. Theory of embryogenesis: Müllerian ducts developed, the medial tract descended to the urogenital sinus. The right tract reached the sinus to rudimentary horn and its uterosacral ligament but failed to develop cervix. The left pair failed to reach the urogenital sinus and underwent atresia. Then failure of canalization is without the agenesis of one horn, the probable result would have been uterus didelphys. We do not have the histology diagnosis so cannot rule out the type of anomaly that may also favour a rudimentary horn on the left and atrophic on the right. However, normal ovaries bilaterally support the failure of fusion and canalization, rather than atrophy. Conclusion: Pathogenesis of this anomaly is unclear, but its discussion helps demonstrate the embryology of the Mullerian tracts. Treatment continues to be unsatisfactory in these cases, and would probably require in-vivo intervention in the first weeks of the embryonic period.