There has been an apparent increase in the frequency and duration of El Niño–Southern Oscillation events in the last two decades relative to the prior period of record. Furthermore, 1990–95 was the longest period of sustained high Darwin sea level pressure in the instrumental record. Variations in the frequency and duration of such events are of considerable interest because of their implications for understanding global climatic variability and also the possibility that the climate system may be changing due to external factors such as the increased concentration of greenhouse gases in the atmosphere. Nonparametric statistical methods for time series analysis are applied to a 1882 to 1995 seasonal Darwin sea level pressure (DSLP) anomaly time series to explore the variations in El Niño–like anomaly occurrence and persistence over the period of record. Return periods for the duration of the 1990–95 event are estimated to be considerably smaller than those recently obtained by Trenberth and Hoar u... Abstract There has been an apparent increase in the frequency and duration of El Niño–Southern Oscillation events in the last two decades relative to the prior period of record. Furthermore, 1990–95 was the longest period of sustained high Darwin sea level pressure in the instrumental record. Variations in the frequency and duration of such events are of considerable interest because of their implications for understanding global climatic variability and also the possibility that the climate system may be changing due to external factors such as the increased concentration of greenhouse gases in the atmosphere. Nonparametric statistical methods for time series analysis are applied to a 1882 to 1995 seasonal Darwin sea level pressure (DSLP) anomaly time series to explore the variations in El Niño–like anomaly occurrence and persistence over the period of record. Return periods for the duration of the 1990–95 event are estimated to be considerably smaller than those recently obtained by Trenberth and Hoar u...