Multigroup calculations of neutron flux and current in the reflector of a thermal reactor may be seriously in error at intermediate neutron energies. This is a consequence of the assumed linear flux variation with lethargy within each group that is implicit in the multigroup method. As a result, most multi-group treatments show marked deviations from age theory at distances of several slowing down lengths (or more) from the source region. Calculations have been made to show the variation of the error in a particular multigroup treatment as a function of distance from the source (measured in slowing down lengths) and of the number of groups.