This note describes and applies a test for trend in the frequency of E
l Nino events over the period 1525-1987. Although there appears to hav
e been a significant increase in frequency over this period, this resu
lt is consistent with an overall increase in the completeness of the h
istorical record. When the analysis is repeated for the later part of
the period and for strong events alone, no significant trends are foun
d.