A Fabry-Perot interferometer has been gathering F region wind data at Millstone Hill routinely since mid-1988. A total of 27 nights of optical data have been collected with simultaneous incoherent scatter radar data. Data for 22 nights (of which 10 were geomagnetically quiet and 12 were unsettled) have been used to evaluate the O+-O collision frequency. Our data show that the collision frequency based on Dalgamo's adjusted theoretical value (Dalgamo, 1964) that was used at Millstone Hill Observatory before 1988 should be increased by a factor of 1.9¿0.15. ¿ American Geophysical Union 1991