To follow the health of the coral reefs of Bonaire and Curacao a number of locations on each island are photographed each year. At each location a 3 m square at up to 4 different depths is recorded and analysed down to species level. The work was started in 1973 and the collected coral data are now the longest time-series of a living reef in the world. The trends show that since 1973 living coral cover has gradually decreased. Most likely causes are coastal development and over-fishing, aggravated by bleaching events during episodes of high sea water temperature and disease outbreaks.