Seven years of data are used to examine the orbital characteristics of five NOAA satellites and the implication for using AVHRR data in climatological studies is investigated. Generally a steady drift from a nominally Sun-synchronous orbit results in the earlier arrival of even-numbered satellites and the later arrival of odd-numbered satellites. The most extreme example of drift, for the case of NOAA-6 resulted in a difference of average arrival time of 90 minutes over the operational lifetime of the satellite. Phasing results in a ±51 minute variation in arrival time. The combination of drift and phasing can have a significant effect on the use of AVHRR and other NOAA satellite data in climatological studies, particularly for the mid- and high-latitudes during the winter and summer solstices.