Spatial disorientation (SD) was the third highest "cause" of fatal accidents in small, fixed-wing aircraft and closely related to the second highest "cause"--"continued VFR flight into adverse weather." SD was a cause or factor in 16% of all fatal accidents. When SD was ascribed as a cause or factor in an accident, 90% of the time that accident involved fatalities. Small, fixed-wing aircraft under 12,500 lb (570 kg) accounted for 97.3% of all SD accidents. Inclement weather was associated with 42% of all fatal accidents, and SD was a cause or factor in 35.6% of these. Flight was initiated into and continued into adverse weather in 19.7 and 68.7%, respectively, of SD weather-related fatal accidents. Fog (56.8%) and rain (41.8%) were the most prevalent adverse weather conditions. These and other data attest to the importance of this psychophysiological phenomenon in flight safety.