In this paper obsolescence of service parts is analyzed in a practical environment. Based
on the analysis, we propose a method that can be used to estimate the risk of obsolescence
of service parts. The method distinguishes groups of service parts. For these groups, the
risk of obsolescence is estimated using the behavior of similar groups of service parts in
the past. The method uses demand data as main information source, and can therefore be
applied without the use of an expert's opinion. We will give numerical values for the risk of
obsolescence obtained with the method, and the e®ects of these values on inventory control
will be examined