Measurements from the Halogen Occultation Experiment (HALOE) are used to infer profiles of aerosol extinction at five infrared wavelengths. This paper provides a validation of the aerosol measurements based on uncertainty analysis, internal validations, comparisons with theory, and comparisons with independent measurements. Monte Carlo calculations using accepted values of random and systematic errors determine typical measurement uncertainties of less than 15% for pressures from 100 to 10 mbar. Comparisons of coincident HALOE sunrise and sunset observations indicate systematic differences (sunrise>sunset) for pressures less than 10 mbar. Random sunrise-sunset differences, taken as an upper limit of the measurement precision, are generally from 10 to ~30% for pressures from 100 to 10 mbar. Measured extinction ratios are compared with ratios determined from theory. These comparisons show that the measurements are consistent with theory at pressures from 100 to 10 mbar, depending on channels, latitude, and season. HALOE extinctions are compared with extinctions calculated from balloon-borne particle counter measurements. The results show random differences from 30 to 50% for pressures from 100 to 10 mbar and systematic differences (HALOE>particle counters) for pressures less than 40 mbar. The results indicate that the HALOE 2.80 μm aerosol measurements are much less reliable than the other four measurements. ¿ American Geophysical Union 1996