The spatio-temporal patterns of seismic activity for events with body wave magnitude mb≥4.0 are investigated for the three most recent large earthquakes in the Oaxaca region of southern Mexico (August 23, 1965, Ms=7.6, Mw=7.5; August 2, 1968, Ms=7.1, Mw=7.3; November 29, 1978, Ms=7.8 Mw=7.6). A master catalogue of earthquakes is compiled for the analyses, using the International Seismological Center (ISC) catalogue supplemented by the National Earthquake Information Service (NEIS) catalogue; the events are then relocated with the Joint Hypocenter Determination (JHD) method. At this magnitude threshold, we find that the aftershock zone of the 1965 earthquake was seismically quiescent for at least 20 months prior to the main event; the 1968 earthquake was preceded by 1 year of foreshock type activity clustered in the aftershock zone; the 1978 earthquake was preceded by 43 months of quiescence and one event (mb=4.7) within the aftershock zone 4 months prior to the mainshock. We also find that a segment of the subduction zone in Oaxaca remains unbroken by these earthquakes. In addition, some catalogue problems are pointed out which are important to interpretations of seismicity patterns.