The autokinetic phenomenon is the visual experience of apparent movement of a stationary object, and can be observed most effectively by looking at a fixed pin-point light in a totally dark room.The phenomenon is offered here as a projective measure of personality structure, and in this sense is used as a diagnostic indicator in mental illness. The test has a proven high reliability. An index figure into which various aspects of the movement pattern is calculated is used for each subject. The movement is more pronounced in schizophrenia, epilepsy, psychasthenia, neurasthenia and anxiety states. In the manic-depressive and involutional psychoses, and in conversion hysteria, movement is, as a rule, either absent or much less extensive.Atypical test results are discussed in the light of more detailed diagnostic opinions of the staff of the hospital in which the tests were given. Prognostic indications are found in the extent and patterns of movement. Limited or medium amount of movement may be considered prognostically more favorable than extensive or no movement. Fairly accurate limits, expressed in indices, have been established in this connection. Erratic movement patterns presage, on the average, a less favorable course of illness. Sex differences are shown in that more men than women observe autokinetic movement.Under comments some implications and analogies are presented to show relationships between autokinesis and mental disturbances, and some suggestions are offered for further investigation.