The South American Monsoon System (SAMS) is characterised by intense convective activity and precipitation during austral summer. This study investigates changes in the onset, demise and duration of SAMS during 1948–2008. The results show a significant change in these characteristics in the early 1970s. Onset becomes steadily earlier from 1948 to early 1970s and has occurred earlier than 23–27 October after 1972–1973. Demise dates have remained later than 21–25 April after the mid-to-late 1970s. SAMS duration shows a statistical changepoint in the summer of 1971–1972 such that the mean duration was ∼170 days (1948–1972) and 195 days (1972–1982). Vertically integrated moisture flux is used to diagnose changes in mean state and reveal statistically significant increases over South America after 1971–1972. Copyright © 2010 Royal Meteorological Society