Tropical lower mesospheric ozone concentrations determined from ultraviolet sunset occultations demonstrate latitude dependent variations from 1985 through 1988. Although there is no detectable secular change at the equator, at 20¿N there is an increase of 1.4% per year, while at 20¿S there is a decrease of 0.6% per year. At all observed latitudes, annual and semiannual oscillations are evident, but the amplitude of the oscillations is a factor of four smaller at 20¿S than at 20¿N. The annual and semiannual ozone behavior is caused primarily by equatorial temperature waves. Secular changes are the result of variations in mesospheric temperature, solar flux, and trace constituents which are involved in the ozone chemistry. The variation with latitude of the observed ozone trends between 1985 and 1989 is different from predictions of some models which simulate stratospheric and lower mesospheric ozone behavior over a sunspot cycle. This is the result of differences between the actual temperature structure of the atmosphere and that adopted in the models, rather than an error in the underlying photochemistry. ¿ American Geophysical Union 1990