This report reviews the availability of data describing penguin abundance in the CCAMLR Convention area, and the uncertainties in deriving overall abundance estimates from these counts. Counts of breeding colonies are available from a variety of sources and, when combined, coverage is thought to be reasonably comprehensive for some areas, but less complete for others. One key problem is that counts have been collected using various demographic units, and the timing of these have varied relative to availability of these units. Counts therefore have to be standardised prior to being summed, but the adjustment data required to achieve this are only available for a small number of site-year combinations. The other fundamental problem is that the latest site counts are of variable ages, and since penguin populations are known to vary with time the assumption of population stability since the most recent count cannot always be justified. Modelling approaches that may reduce these uncertainties are recommended and the errors and biases that are likely to arise from fitting these to penguin count data are discussed.