We have been operating a ground-based microwave radiometer for the 22.235 GHz water vapor line at the ALOMAR observatory, Norway, in 1995/96 and continuously since July 1997. Its high latitude location (69 ¿N, 16 ¿E) provides a new and unique dataset of stratospheric and mesospheric water vapor observations. We briefly describe our instrument and measuring technique and present the data of our ongoing measurements. The water vapor mixing ratio shows a pronounced annual cycle that is stronger than what has been reported for mid-latitudes. We also present an analysis of our data for the upper mesosphere for the relationships between mesospheric water vapor, temperature, polar mesosphere summer echoes (PMSE), and noctilucent clouds (NLC) during summer months. This investigation indicates that water vapor is already present near mesopause heights when the PMSE/NLC season starts and is still present long after it has declined. ¿ 1999 American Geophysical Union