A reliability generalization study was conductec on data from 69 samples found in 44 studies that employed the Psychoticism (P), Extraversion (E), Neuroticism (N), and Lie (L) scales of the Eysenck Personality Questionnaire (EPQ) or EPQ-Revised. The reliability of the scores varied considerably between scales, with P scores tending to have the lowest reliability. Hierarchical regression analyses revealed that a larger standard deviation of scores was associated with higher score reliability for all four EPQ scales. More variability in age was associated with higher score reliability for the P scale and the L scale. Samples composed of students provided scores with higher reliability than those composed of other types of individuals for the P scale. Several other potential predictors (form, language of administration, average score average age, gender composition, and number of items per scale) were not significantly related to score reliability.