Multicolour flow cytometry in haematology has developed considerably in recent years. The ability to analyse eight or more colours of fluorescence on millions of cells in a matter of minutes has enabled the provision of rapid and reliable measures of minimal residual disease for clinicians. The use of multicolour analysis has also enabled more specific characterisation of presenting leukaemias and lymphomas. However, there has not been a concomitant increase in the knowledge and experience of the flow cytometrists to deal with certain problems associated with this more complex analysis.