Frequency distribution of the length of time until fixation (excluding the cases of eventual loss) of a selectively neutral mutant in a finite population was obtained. With 4Ne generations (Ne, effective population size) as the unit length of time, the distribution has mean μ1 = 1, standard deviation σ = 0·538, skewness γ1 = 1·67 and kurtosis γ2 = 4·51 (see Fig. 1).