Global cloud cover has been monitored with multi-spectral observations from the eleven polar orbiting HIRS (High resolution Infrared Radiation Sounder) since December 1978. The HIRS longwave infrared data have a higher sensitivity to semi-transparent cirrus clouds than visible and infrared window techniques. Clouds are found in 71% of all HIRS observations from 65 S to 65 N; high clouds are observed in 33% of the observations. Closer investigation of the tropics indicates that there has been little overall change in the global cloud cover. There is the possibility of a small increase in high cloud cover from the first decade to the second (~2%) however orbit drift of some sensors and instrument differences may be part of this. Significant weather events such as El Nino Southern Oscillation or volcanic eruptions may also be influencing the trends local areas but show little signal in global averages.