Models were developed to predict the tenure status of 106 psychiatric nursing assistants at 3, 6, and 12 months after beginning employment at a large public psychiatric inpatient facility. The attrition rate of this sample was 40% which was consistent with trends reported in the literature. The predictive power of four groups of variables—personal, training, ward related, and organizational—was shown to change over time. Personal and training variables were significant early determinants of tenure, while ward and organizational factors gained more importance during the course of the year. Certain factors that appear important in reducing turnover of nursing assistants are discussed, with recommendations for program changes.