A data set of 3637 records collected on two Polish fox farms in 1985-1999 was used to estimate variance components and genetic trends in a population of the silver fox. In order to evaluate the effect of the new grading standard (introduced in 1997) on variance components and genetic progress, the trait scores from the original data set were transformed into scores of the new grading standard. Variance components were estimated by the restricted maximum likelihood (REML) method using the average information (AI) algorithm. A linear model that included herd, year of birth and birth season as fixed effects and additive genetic was used as a random effect. The annual genetic trend for the studied traits was estimated as regression of breeding value on time. It was found that the new grading standard had a small effect on variance components and derived heritabilities of the traits. The estimates of heritability derived from the original data ranged from 0.182 (±0.031) to 0.553 (±0.040), and although somewhat higher, were comparable to those derived from the transformed data, which ranged from 0.190 (±0.032) to 0.355 (±0.039). The genetic trends estimated for the traits graded according to the old grading standard ranged from -0.019 to 0.231, and in general were higher than those estimated for the traits evaluated according to the new grading standard (ranging from -0.007 to 0.167).