Estimates of the union wage premium for US workers are presented based on longitudinal data from the 1979 cohort of the National Longitudinal Survey of Youth. Our results indicate that the long-term private-sector union wage premium for men has remained fairly steady at nearly 22% over the period 1990 to 2010. For women, the wage premium exhibits greater volatility, although no clear downward trend, and is approximately one-half of the male premium.