The heritability of minimum weight for onset of sexual maturity in chickens (WTSXM) and its phenotypic and genetic correlations with early growth rate were studied in a Leghorn (L) layer stock, in two White Rock (WR) broiler stocks, and in the F4, F5, and F6 segregating generations of a White Rock X Leghorn (WR X L) cross. Mean heritability of WTSXM was .38 in the WR populations and .84 in the WR X L cross populations. Mean WTSXM of the various genetic stocks were closely related to their mean early growth rate. The mean phenotypic correlation of WTSXM and early growth rate was .07 in the WR populations but .47 in the WR X L cross populations. Estimates of the genetic correlation of WTSXM with early growth rate were high, and uniform in sign in the WR X L cross populations but smaller in magnitude and variable in sign in the WR populations. The implications of these results with respect to WTSXM as a breeding objective are discussed.