The purpose of this study was to determine the environmental properties of sorted and aged bottom ash from municipal solid waste incineration (MSWI BA) and the significant variations in these properties between four plants and four different sampling periods over one year. The non-magnetic 0–50 mm fraction, stored outdoor in 10m3 boxes for six months, was used. Duplicate samples of the materials were tested for total content and potentially-leachable amounts, with and without oxidising conditions. Inorganic components were analysed. The results were evaluated by means of an analysis of variance and factorial design evaluation. The total content of the samples was dominated by Si, Ca, Fe and Al. Significant differences were found between plants and samples with regard to major component content. The minor components were dominated by Zn, Cu and Pb although significant differences between plants or samples were difficult to identify for Cu and Pb. The potentially-leachable amounts were dominated by Ca for the major components and Cu and Zn for the minor components. Precision in potential leachability was lacking, especially for Cu and Pb. Oxidised conditions increased the leachability of Cr significantly and in some cases also Cu. The overall conclusion from the study was that the results from the determination of total composition or potentially-leachable amounts of minor components need to be evaluated statistically and that comparisons with limit or guideline values need to take the significance of the measured values into account. The experimental errors should be evaluated separately for each element. Moreover, the experimental errors were not a direct function of the average total or leached amounts. Differences in weathering products in the aged material that carried the elements studied also seemed to have an impact on the error in the measurements.