Examination of polycarbonate track-etched membranes by electron microscopy and image analysis allowed the pore size analysis to be extended to the quantification of the pore shape and spatial distribution of the pores. It was possible to distinguish different shapes, such as multiplet classes by use of the longest dimension in addition to the diameter of a circle of equivalent area. It was shown how the pore shape distribution changed for a series of membranes of increasing porosity. Porosity was very difficult to quantify accurately, since it embodied variabilities of both the pore size and pore density. Variation in the pore size distribution was shown to account for both the scatter and deviation from linearity in the relationship between the pore density and porosity, even though it had previously been considered that the pore size of the lower porosity track-etched membranes was nearly ideally narrow. All membranes were found to be heterogeneous in all variables at the magnifications employed. Statistical analysis of replicate measurements, with up to ten samples per membrane and ten images per sample, permitted estimation of sampling plans necessary to achieve specified accuracy in characterisation of mean pore size, pore density and porosity, as may be required for statistical process control of membrane qualities.