The purpose of the present longitudinal study was to investigate the stability of backward masking performance in schizophrenics and nonschizophrenic psychotic patients. Twenty-two schizophrenics, eight nonschizophrenics, and 14 normal controls were tested three times, with an interval of 1 year between each test session. A standard stimulus duration procedure was used. The relative onset intervals between the target and the mask was 16.5 msec or 33 msec. A no mask condition was presented before the two masking conditions. Results showed that masking performance is a stable phenomenon, for both psychiatric groups and for normal controls. Significant differences were found between schizophrenics and the normal controls, but not between the two psychiatric groups. Vulnerability to masking stimuli as a specific characteristic for schizophrenics is, thus, not supported in the present study. The results suggest that backward masking deficit is an enduring feature of psychotic disturbances.