Two problems relating to segregation analysis for Wilson's disease are discussed 
and a practical solution is presented. A problem in the ascertainment of 
families with Wilson's disease is illustrated by comparing segregation ratios 
calculated by the single selection, complete truncate, and multiple incomplete 
selection methods. The effect on the segregation ratio of exclusion from the 
analysis of those sibs who had died of other diseases at a young age is also 
discussed and a method of adjustment of the number of the affected using the 
data on age at onset is proposed. The segregation ratio by multiple incomplete 
selection (Weinberg proband method) after adjustment for those sibs who had died 
of other diseases was 0.243, consistent with the theoretical value for autosomal 
recessive inheritance. The segregation ratio calculated by the single selection 
method tended to give a lower value, while that calculated by the complete 
truncate method was greater than the theoretical value. Recessive inheritance 
is, however, supported. The actual effect of exclusion of those sibs who had 
died of other diseases on gene frequency estimation is shown to be very small.