In a previous study, one of the authors (C.C.B.) found isolated sleep paralysis was common in blacks. In this study, conducted by interviews, a recurrent pattern (one or more episodes per month) of isolated sleep paralysis episodes in blacks was described by at least 25 percent of the afflicted sample studied. Frequent episodes were associated with stress, and subjects with isolated sleep paralysis had an unusually high prevalence of panic disorder (15.5 percent). The genetic transmission of sleep paralysis was studied in a large black family, and in addition to stressful environmental factors being associated with the condition, there appears to be a dominant genetic factor associated with the predisposition for developing sleep paralysis. The implications of these findings for stress, anxiety, sleep, and psychophysiologic disorders are discussed.