An approximation of the exact distribution of the Wilcoxon test for symmetry by means of an Edgeworth series is derived. Probabilities are computed for sample sizes N = 10(1)26(2)42(3)48,50,100, and the accuracy investigated and compared with that of the normal approximation. The Edgeworth expansion gives a very satisfactory approximation for N ≥ 15 (maximum error < 25×10−5 when taken to terms of order 1/N and < 6×10−5 to terms of order 1/N2, for a standardized variable (x) in the region 1.75 ≤ x ≤ 3.1). For N = 20 the Edgeworth approximation almost coincides with the exact distribution. For N > 20 where no exact probabilities are readily available, the accuracy of the normal distribution is investigated relative to the Edgeworth expansion to terms of order 1/N2. The validity of this procedure is established by calculating certain exact probabilities in the interval studied, for values of N = 21, 22 and 25. The Edgeworth expansion to terms of order 1/N is readily computed and gives the same degree of accuracy when N = 15 as that given by the normal distribution when N = 100.