We describe satellite observations and analyses leading to the abundance of neutral atomic hydrogen near 300 km and its horizontal distribution with latitude and local time through the summer thermosphere. These H concentrations were derived from the charge-exchange equilibrium relationship between hydrogen and oxygen atoms and ions, with basic in situ measurements accomplished in the F region with the AE-C satellite around the June 1974 solstice near a solar minimum. Critical observational information concerning the low ion densities of H+ was provided by the magnetic ion mass spectrometer (MIMS) on board this spacecraft. A partitioning of the available database serves to illustrate the dirunal variability of thermospheric hydrogen in several prechosen zones of latitude to the 68¿ orbital inclination of AE-C; an alternative approach accentuates the dependence on latitude in select local time intervals. Observed seasonal changes reflect a general decrease in hydrogen density from the equatorial region toward the summer pole, with the largest latitudinal gradients near predawn and the smallest during afternoon. We demonstrate reasonable consistency of the broad horizontal behavior with other available observations and the mass spectrometer/incoherent scatter 1986 atmospheric model, both for the extensively studied diurnal variation at low latitude and the lesser-known latitudinal dependence. Of special significance are apparent effects on the thermospheric H abundance and distribution associated with several geomagnetic disturbances during the extended time period of data acquisition. These features are most discernible as perturbations in the recorded dirunal variation but also alter the latitudinal gradients. We include a brief discussion regarding the observed relationship between local H concentration and the temperature as they vary through the summer thermosphere, noting distinctly different power law behaviors in the hydrogen distribution for temperatures lesser and greater than ~800 ¿K. ¿ American Geophysical Union 1995