AIMS: To reconstruct the arrangement in space of all major ducts and their branches from nipple to periphery of a human breast obtained at necropsy. METHODS: Duct tracing through cleared haematoxylin stained 2 mm sub-gross coronal slices of a complete necropsy breast and computer modelling of duct territories. RESULTS: All branches were traced for 10 complete duct systems of a single breast from a 19 year old girl. Their complexity prevented comprehensive modelling of individual ducts and rami using available computer software, but the territories (catchments) drained by individual duct systems did not overlap and could be reconstructed. Catchment volume and length of the central unbranched duct draining each catchment varied greatly. Duct spacing showed non-random uniformity which is also seen in rodent mammary glands. CONCLUSIONS: These spatial relations are consistent with mutual growth inhibition between duct systems during mammary development. Although there is no clear morphological distinction between mammary duct end buds and lateral buds in women, the present study does suggest that processes of branching morphogenesis occurring during development of the breasts in women do show some analogies with the growth of end buds/lateral branches/alveoli during rodent mammary gland development. Rodent models of mammary development may usefully suggest hypotheses about human breast biology. Less laborious methods of three dimensional reconstruction of mammary ducts and their branches from sub-gross slices, allowing more specimens to be studied, would be valuable for the study of normal human breast development and mammary intraepithelial neoplasia. Increasing power and decreasing costs of high definition image processing hardware and software may make such endeavours practicable.