Technical Abstract: Objectives of this research were to estimate heritabilities of scrotal circumference and semen traits, and genetic correlations between these traits and birth weight. Line 1 Hereford bulls (n = 841), born in 1963 or from 1967 to 2000, were selected either for use by USDA-ARS at Miles City, Montana or for sale. Semen was collected by electro-ejaculation when the bulls were approximately one year of age (mean = 446d) and all samples were evaluated by one person. Traits analyzed were scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities. Primary abnormalities were abnormal heads, abnormal mid-pieces, and proximal droplets. Secondary abnormalities were bent tails, coiled tails, and distal droplets. Data were analyzed using MTDF-REML. The model included fixed effects for contemporary group and age of dam, covariates for age of bull at evaluation and inbreeding of the bull and his dam, and random animal and residual effects. Random maternal effects were also included for birth weight. Heritability estimates for birth weight, scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities were 0.46, 0.57, 0.09, 0.16, 0.22, 0.34, 0.23, 0.09, and 0.13, respectively. Estimates of genetic correlations between birth weight and scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities were 0.36, 0.07, 0.58, 0.21, 0.20, 0.34, -0.25, and 0.05, respectively. The moderate estimates of heritability for many of the traits indicate potential for favorable selection response. Positive genetic correlations between birth weight and majority of the traits suggest selection to reduce birth weight may compromise semen traits. However, for most traits the expected correlated responses are small.