This study reports a 30-year follow-up of 107 former high school juniors and seniors from a rural Midwestern community who completed the Kuder Occupational Interest Survey (KOIS) in 1975 and 2005. Absolute, intra-individual, and test-retest stability of interests, and predictive validity of occupations were examined. Results showed minor absolute (mean) changes, moderate intra-individual stability (Spearman rho = 0.54), and scale test-retest correlations ranging from 0.10 to 0.76. This study corroborates earlier stability studies and extends our understanding of why some individuals show unstable interest patterns. Several Time 1 KOIS interest scores correlated with intra-individual stability itself. Comparisons between 1975 KOIS scores and 2005 occupation using the Brown-Gore C-index demonstrated predictive validity by yielding fit indices for women and men exceeding the theoretical mean. Findings inform our understanding of midlife career development and have implications for career counseling practice. (Contains 4 tables and 1 figure.)